Four-dimensional (4D) printing, as an advanced additive manufacturing technology, enables the fabricated structures to undergo programmable shape or performance changes over time in response to external stimuli. This technology has a significant application potential in aerospace, communication, and biomedical engineering. However, achieving ceramic structures with high precision, complex shapes, and excellent shape memory functionality remains a major challenge. The main difficulty lies in the inability to formulate ceramic slurry suitable for high-resolution printing and precisely controlling the shape memory behavior of the printing precursors and the sintering process. To address these challenges, this study was to use a photopolymerization 4D printing technique to prepare alumina ceramic precursors with shape memory effects. An effective printing of ceramic specimens was ensured via formulating high-solid-content ceramic slurry and optimizing their rheological properties. The shape memory performance was characterized, and the debinding and sintering strategy was adopted based on the results of thermal analysis to obtain dense and crack-free ceramic parts. Also, the shape recovery was achieved through Joule heating, having an application potential of the ceramic precursors in aerospace intelligent hinges. This study could provide a feasible technical approach for designing and manufacturing shape memory ceramic structures through 4D printing and offer practical methods for developing advanced intelligent ceramic components.

For the preparation of the ceramic slurry, polyurethane acrylate, acrylic isoprene ester, and ethyl (2,4,6-trimethylbenzoyl) phenylphosphoric acid ester were mixed in a weight ratio of 51∶45∶4 to prepare the shape memory polymer (SMP) resin. Afterwards, the SMP resin was mixed with alumina powder in a weight ratio of 55∶45, and was stirred by a mechanical mixer under heating and ultrasonic vibration for 30 min to obtain a uniform ceramic slurry. The rheological properties of the slurry were tested using a rotational rheometer. The 3D printing was completed by a vat photopolymerization (VPP) printer, with the process parameters including a layer thickness of 50 μm, a laser power of 100 mW, and a scanning interval of 0.03 mm. To characterize the shape memory performance, the rectangular samples (1.5 mm×5.0 mm×30.0 mm) were heated at 80 ℃ to deform, and then cooled to 25 ℃ to fix the temporary shape. The shape fixation rate (R_f) and shape recovery rate (R_r) were calculated based on the shape fixation angle and shape recovery angle, and 10 cycles of tests were conducted. The glass transition temperature (T_g) of the printed precursor was determined by a dynamic thermal mechanical analyzer (DMA). The chemical structure evolution before and after curing was analyzed by Fourier transform infrared spectroscopy (FTIR). The potential applications in fields such as aerospace intelligent hinges were initially demonstrated under the influence of Joule heating. The temperature rise rate was tested by thermogravimetric differential scanning calorimetry (TG-DSC) in a nitrogen environment at a rate of 10 ℃ per minute, starting from 30 ℃ to 800 ℃, to guide the debinding and sintering processes.

The prepared ceramic slurry exhibits a distinct shear-thinning behavior, with decreasing viscosity significantly as the shear rate increases, making it suitable for use in UV photopolymerization-based printers. The dynamic thermomechanical analysis reveals a glass transition temperature (T_g) of approximately 76.24 ℃ for the ceramic precursor. The printed precursor demonstrates excellent shape memory properties, achieving R_f and R_r rates of approximately 97% and 98%, respectively, for 10 test cycles, confirming stable and reliable shape memory performance. The Fourier transform infrared spectra confirm that the ceramic slurry successfully undergoes a photopolymerization and forms a cross-linked network. Furthermore, complex structures such as box and flower models are successfully printed, and they show the excellent shape recovery under thermal stimulation, highlighting a flexibility of this process for fabricating intricate shapes. The study utilizes the Joule heating as an external stimulus to drive shape recovery, demonstrating a potential of ceramic precursor as an intelligent hinge for aerospace applications. The thermogravimetric-differential scanning calorimetry indicates key temperature stages for organic component decomposition. In addition, a debinding and sintering strategy is implemented, effectively preventing cracking and deformation, and yielding dense, crack-free alumina ceramic parts.

This study fabricated an alumina ceramic precursor with a shape memory effect by the photopolymerization 4D printing technology, and systematically investigated its printing process, shape memory performance, and sintering behavior. The study demonstrated that the configured ceramic slurry had excellent shear thinning properties and rheological performance, making it suitable for high-precision stereolithography printing. The precursor printed was found to exhibit a significant shape memory function, with a shape fixation rate of approximately 97% and a shape recovery rate of approximately 98%. It could be controlled to undergo shape reconstruction and recovery through thermal stimulation. The shape recovery of the precursor structure was achieved through the Joule heating, demonstrating its potential application in fields such as aerospace intelligent hinges. Moreover, the thermal analysis results indicated that the optimized degreasing and sintering process could yield structurally complete and dense ceramic parts. This research could provide a feasible technical approach for 4D printing of ceramic materials and the design of shape memory structures, having a significant theoretical and application value.

Graphene/SiC composites are widely used in the fields of filtration, biomedicine, catalysis, microwave absorption, energy storage and chemical sensing. 3D printing technology can realize the design of fine feature change and integrated molding complex geometric structure in the preparation of porous ceramic materials, especially the slurry direct writing process (DIW). The physical properties and other functions of composites strongly depend on the microstructure obtained during processing, so these phenomena must be systematically investigated to design and produce reliable materials, especially for 3D printing applications. In this paper, graphene/SiC matrix composites were prepared by DIW technology, and their printing accuracy, microstructure, pyrolysis behavior, mechanical properties and electrical properties were investigated.

SiC powder with an average particle size of 3.2 μm was used as a matrix of the composite. A graphene powder with average particle size of 8 μm, bulk density of 0.08-0.13 g/mL, thickness of 1-3 layers and purity of 99% was a reinforced phase. Polycarbosilane (PCS) with a molar mass of about 1500 g/mol was used as a precursor to prepare ceramic slurry. The diameter of extrusion nozzle was 0.55 mm, the layer thickness was 0.48 mm, and the printing speed was 6 mm/s, which was used for DIW. The morphology and distribution characteristics of graphene in the cross section of graphene/SiC_p composite extruded wire were characterized by scanning electron microscopy (SEM). The phase composition of graphene/SiC matrix composites after pyrolysis was determined by X-ray diffraction (XRD) with Cu K_α - ray (λ), the scanning rate of 10 °/min, and the scanning angle (2θ) of 20°-80°. The Raman spectra of graphene/SiC matrix composite samples were analyzed by Raman spectroscopy in a scanning range of 1000-2000 cm^-1, power of 10 MW, and laser wavelength of 532 nm. The resistance of single wire after pyrolysis was measured by inductance capacitance meter (LCR) and the conductivity was calculated. The tensile test was carried out in an electronic universal testing machine, the tensile rate was 0.1 mm/min, and the tensile strength was calculated. A universal testing machine was used to carry out compression test on the pyrolytic frame samples, and the displacement speed was 0.2 mm/min. The compressive strength was calculated.

The experimental results of single-layer printing and dot matrix structure printing show that all three slurries exhibit a good extrusion forming ability. In addition, increasing the graphene content in the slurry can suppress the spreading deformation of extruded filaments, reduce the line width, and make it closer to the extrusion diameter, which is helpful for high-precision printing. The SEM images of the extruded filament cross-section show that the graphene layers form a certain degree of orientation in the matrix. In the central region, there is a relatively random and irregular arrangement, and the orientation of graphene sheets is most pronounced in the edge region. At the central axis, the shear rate is rather low, the orientation torque is weak, and the graphene layers are randomly distributed mainly due to the non-uniform shear flow field experienced by the slurry in the extrusion port. In the edge region, the shear rate is extremely high, forcing the graphene layers to deflect and arrange along the streamline direction. The pyrolysis process forms a porous structure, and the graphene layers are well preserved. In the Raman spectra, the I_D/I_G value of 25G is the smallest, and the higher the graphene content, the lower the average defect density of graphene. The higher the graphene content, the higher the tensile strength of the extruded filament and the compressive strength of the lattice structure.

The DIW process using graphene/SiC_p/PCS composite slurry could achieve the preparation of lattice grid structure green bodies. The printing ability of the slurry improved with the increase of graphene content. In the DIW printing process, graphene layers were oriented and arranged along the extrusion direction in the extrusion filament, forming an orientation gradient structure from the center to the edge, and the higher the content, the more significant the orientation characteristics and gradient. Graphene improved the strength of composite materials via constructing gradient orientation distribution, enhancing interfacial bonding, and exerting crack bridging effect. Also, it significantly improved the conductivity of porous SiC based composite materials. At the graphene content of 25%, the tensile strength of the extruded filament and the compressive strength of the lattice structure could be the maximum values, and the electrical conductivity of a single filament reached 247.1 S/m, providing a feasible material system and technical path for the development of multifunctional lightweight ceramic materials for extreme environmental applications.

Lead zirconate titanate (PZT) piezoceramics are widely used in sensors, actuators, and energy harvesters because of their intense electromechanical coupling. As device designs shift toward porous structures, curved parts, and lattice architectures, conventional ceramic processing becomes less practical due to the brittleness, tooling limits, and mold cost. Vat photopolymerization (VPP) additive manufacturing can produce high-resolution parts with a good surface quality, yet PZT printing is often limited by poor curing. Pre-sintered PZT powders can absorb and scatter UV light, which reduces curing depth, weakens interlayer bonding, and causes lateral overcuring that blurs feature edges.

To mitigate these issues, this study was to introduce an integrated "inorganic-precursor photopolymerization + solid-state reaction" route. ZrO₂-TiO₂-PbCO₃-based precursors could replace presintered PZT to improve optical penetration and curing stability during VPP. Meanwhile, La₂O₃ served as a multifunctional dopant to favor sharpen printed features via limiting lateral curing spread, promoted densification, refined grains, and tuned tetragonal-rhombohedral coexistence toward an MPB-adjacent state during sintering. This study could provide a practical way to improve both printability and ferroelectric/piezoelectric performance.

Pb_1-xLa_xZr_0.53Ti_0.47O₃(i.e., x=0、0.01、0.02、0.03、0.04、0.05) precursor powders were prepared via stoichiometric mixing of ZrO₂, TiO₂, PbCO₃ and La₂O₃ and subsequent grinding to ensure the homogeneity. The photocurable slurries with 82% solids were formulated by a TMPTA/PEG400/modified epoxy/HDDA resin system (in a mass ratio of 3∶3∶3∶1), TPO photoinitiator (3% relative to resin), and dispersant (2% relative to powders). The VPP printing was conducted at 12 mW·mm^-2 with an exposure for 3.5 s per layer. The printed parts were subjected to a staged debinding-calcination-sintering, including debinding in N₂ to 350 ℃ for 2 h and 600 ℃ for 2 h under slow heating to mitigate cracking, followed by air burnout/calcination with holds at 600 ℃ and 850 ℃ and final sintering at 1270 ℃ for 2 h. Silver electrodes were screen-printed, and the samples were poled in an oil bath under 3 kV·mm^-1 at 140 ℃ for 15 min. The curing depth and lateral linewidth were quantified via the Beer-Lambert and Gaussian beam fitting. The density/porosity, scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns (rietveld refinement), P-E loops, dielectric spectroscopy, d₃₃, and the relaxor diffuseness parameter γ were employed to establish the process-structure-property relationships.

Once presintered PZT powders are replaced by inorganic precursors, the most immediate change appears in curing robustness. Under identical exposure conditions, the single-layer curing thickness increases from 25 μm to 80-85 μm, while the optical penetration depth D_p increases from 9.94 μm to 28-30 μm. With much weaker attenuation in the curing band, the chronic issues of insufficient through-thickness curing and limited interlayer bonding are substantially relieved. A stronger curing does not occur at the cost of poorer fidelity. Lateral broadening becomes easier to restrain. The effective beam half-width w_o decreases from 44 μm in a conventional slurry to 15.0 μm in the precursor system, and further decreases to 13.7 μm after La₂O₃ addition, making the linewidth less sensitive to exposure energy and reducing overcuring-driven edge blurring.

La₂O₃ affects printing and sintering, but its sintering benefit appears only within a limited range. The densification improves as La₂O₃ increases, and then declines as the dopant is excessive. The relative density increases from 94.1 to 99.8% and decreases to 97.6% when La₂O₃ exceeds 3%. In parallel, La₂O₃ strongly refines the microstructure, keeping grains with the sizes of 1.27-2.30 μm, while undoped PZT reaches 8-10 μm under the same conditions, indicating a suppressed abnormal grain growth. The Rietveld refinement shows a single perovskite phase for all the compositions, with MPB-type tetragonal-rhombohedral coexistence. The rhombohedral fraction increases to t 22.4% as x = 0.03 (tetragonal of 77.6%) and then decreases at a higher x, indicating an optimal coexistence as x = 0.03.

The electrical properties follow the same peak behavior. The undoped ceramics show low P_r (i.e., 4.07-4.31 μC·cm^-2) and E_c of 0.78 kV·mm^-1, whereas La doping boosts P_r to 32.87 μC·cm^-2 and E_c to 1.18 kV·mm^-1 as x = 0.03. The dielectric response remains stable from 10² to 10⁵ Hz, with ε_r≈(3.0-3.3) × 10³ and tanδ≈0.03-0.05. The piezoelectric coefficient d₃₃ increases from 205 to 350.6 pC·N^-1 as x = 0.03, then decreaes at a higher x. The relaxor behavior strengthens as well, with γ rising from 1.33 to 1.85 as x = 0.03 (1.86 as x = 0.05). The PFM and TEM images indicate that a moderate La₂O₃ enhances domain switching, while an excess La₂O₃ increases disorder and random-field effects, weakening ferroelectric order and reducing P_r, ε_r, and d₃₃ beyond the optimum.

This work combined precursor-assisted VPP printing with solid-state reaction sintering to improve curing stability, dimensional accuracy, and electromechanical performance in PLZT. The precursor increased curing depth, La₂O₃ limited lateral curing, and the dopant refined grains and supported MPB-adjacent phase coexistence during sintering. The overall performance became optimum as x = 0.03, where P_r, d₃₃, and ε_r increased, while dielectric loss was low, although the more relaxor-like behavior indicated a trade-off between higher response and greater disorder.

Tritium breeders are key functional materials for achieving tritium self-sufficiency in the breeding blanket of nuclear fusion reactors. Conventional pebble bed tritium breeders are limited due to an upper bound of packing factor, stress concentration-induced fragmentation, and high gas flow resistance, making them difficult to simultaneously achieve efficient heat and mass transfer, thus restricting the enhancement of tritium production performance. In this study, a design concept employing porous tritium breeders based on triply periodic minimal surfaces (TPMS) was proposed as an alternative to the conventional pebble bed configuration. Typical Gyroid and I-WP structures were selected as research objects, and a flow-solid coupled numerical model under reactor-relevant operating conditions was proposed to systematically compare the sweep gas flow behavior and heat transfer characteristics of the two TPMS structures with those of the conventional pebble bed.

The geometric model of the pebble bed was constructed by discrete element method (DEM), while the Gyroid and I-WP structures were generated based on implicit trigonometric parametric representations. Numerical simulations were performed by a software named Ansys Fluent with the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) model to investigate the flow and heat transfer characteristics of helium within porous microchannels. Gyroid-type porous tritium breeder samples were fabricated by a stereolithography system, and their internal three-dimensional architectures were reconstructed via micro-computed tomography (micro-CT). The pressure drop and effective thermal conductivity of the samples were measured using a helium flow resistance pressure-drop measurement setup and a Hot Disk TPS 2500S thermal conductivity analyzer, respectively.

Compared with the conventional pebble bed configuration, TPMS-based tritium breeders exhibit significant advantages in thermo-hydraulic performance. The Gyroid and I-WP structures both effectively reduce flow resistance and improve flow field uniformity, which is beneficial for sweep gas transport and heat removal. Among the two TPMS configurations, the Gyroid structure demonstrates superior performance. Within the inlet velocity range of 0.1-0.2 m/s, the average flow velocity is increased by approximately 56%, the pressure drop is reduced by 50%, and the effective thermal conductivity is enhanced by 13.7%, compared with the pebble bed. These improvements are mainly attributed to the continuous integrated solid skeleton and the highly interconnected pore network of the TPMS structures. In addition, the Gyroid porous tritium breeder samples are fabricated via additive manufacturing, and the thermo-hydraulic experiments are conducted under representative operating conditions. The experimental results show good agreement with the numerical data, confirming the reliability of the numerical model.

This study targeted breeding blanket applications in nuclear fusion reactors and proposed a TPMS-based porous ceramic tritium breeder design. The thermo-hydraulic characteristics of Gyroid and I-WP tritium breeder structures were systematically evaluated and compared with those of a conventional pebble bed via combining numerical simulations with experimental investigations. The results demonstrated that both TPMS configurations could exhibit significantly lower flow resistance and superior thermo-hydraulic performance relative to the pebble bed, with the Gyroid structure showing the best overall performance. The numerical predictions were in reasonable agreement with the experimental results, confirming the reliability of the developed model and preliminarily demonstrating the engineering feasibility of the Gyroid porous ceramic tritium breeder.

The existing PBAM achieves phased results. To further promote its large-scale application in the fabrication of high-performance ceramic molds, there are the following aspects. There is an urgent need to develop additive manufacturing-specific powders and functional binder systems. For BJAM process, composite ceramic powders with favorable flowability and optimized gradation should be developed, and multifunctional binder systems should be designed to reduce the dependence on post-processing performance regulation. For SLS process, it is necessary to develop ceramic/binder phase composite powders with high laser absorptivity and excellent sintering activity, so as to reduce the difficulty of subsequent sintering and improve the strength of ceramic molds. Dedicated printing systems and post-processing equipment suitable for the multi-material integrated forming of ceramic molds should be developed. Key technologies such as precise multi-material powder spreading and delivery, as well as synchronous manufacturing of ceramic cores and shells, should be prioritized to realize high-precision and high-efficiency integrated forming of ceramic molds with complex structures. Regarding the performance regulation, improving the high-temperature strength, creep resistance and dimensional stability of ceramic molds becomes an emphasis. The porosity and relative density can be synergistically regulated to balance the contradiction between high strength and easy core leaching by means of material design, printing parameter adjustment and post-processing process optimization, so as to meet the stringent performance requirements of ceramic molds for high-end castings.

Future developments in the field are likely to follow three main trajectories. First, standardized definitions and transfer rules for transferable variables are required to reduce inconsistencies among models and to support reproducible coupled workflows. Second, the integration of uncertainty-aware calibration and sensitivity analysis into process-window design is warranted as fundamental constitutive relations and kinetic parameters are constrained by measurement limitations and condition dependence. Third, integrated workflows combining high-fidelity simulation, reduced-order modeling, and data-driven surrogates are essential for fast component-scale screening and optimization. Driven by these advances, full-process modeling can evolve from retrospective interpretation toward prospective control of process-structure-property linkages in ceramic BJ, thereby improving reliability, dimensional fidelity, and performance consistency across diverse material categories.

As one of the new ultra-high temperature structural candidate materials, oxide composite ceramics show great application prospects in the hot-end structural components of a new generation of high-end aerospace equipment due to their excellent high-temperature oxidation resistance, corrosion resistance, and other properties. In recent years, researchers have conducted detailed monitoring on the stability, temperature distribution, and flow mode of the oxide composite ceramics molten pool using monitoring methods such as high-speed cameras, spectrometers, and thermal imaging. This can clarify the microstructure and defect formation process after solidification, and provide rich molten pool information support for the development of numerical simulation. Although significant progress is made in the existing research on molten pool monitoring and regulation, LAM oxide composite ceramics still inevitably have various defects, making their practical application unable to meet the requirements. To break through the bottleneck in the preparation of large-sized complex-structured oxide ceramics, more in-depth and systematic research on the monitoring and regulation of the molten pool prepared by LAM is needed. Future research can focus on the following directions, i.e., 1) Exploring the preparation technology of large-sized complex oxide composite ceramic components and establishing a multi-factor collaborative regulation method for the molten pool; 2) Promoting the integration of machine vision and feedback control to realize intelligent control in the LAM preparation process; and 3) Developing the multi-field coupling numerical simulation technology for LAM oxide composite ceramics, thus providing a theoretical support for in-depth research on the mechanism of defect formation and evolution.

(Hf, Zr)B₂ solid solutions are promising ultra-high temperature ceramics (UHTCs) for hypersonic applications based on the high-temperature stability of HfB₂ and the low cost of ZrB₂, exhibiting superior properties to single-component counterparts. However, a covalent bonding leads to a poor sinterability, making the pressureless densification of pure (Hf, Zr)B₂ a challenge. While B₄C is known as an effective sintering aid for monolithic borides, its role in the densification and microstructural evolution of (Hf, Zr)B₂ solid solutions under pressureless sintering conditions remains unexplored. This study was to investigate the effects of B₄C content (i.e., 0-5%) and sintering temperature (i.e., 1900-2200 ℃) on the densification behavior and microstructure of (Hf, Zr)B₂, to provide theoretical guidance and process references for the pressureless sintering preparation and microstructural control of (Hf, Zr)B₂-B₄C composites.

(Hf, Zr)B₂ powders were synthesized via boro/carbothermal reduction at 1700 ℃ with HfO₂, ZrO₂, B₄C, and graphite as raw materials. The obtained powders were then mixed with 0, 2% and 5% B₄C by milling in ethanol for 12 h, followed by rotary evaporation and drying at 60 ℃. The mixed powders were uniaxially pressed into compacts and subsequently cold isostatically pressed at 200 MPa. The pressureless sintering was conducted in an ultra-high temperature furnace in argon atmosphere at a heating rate of 10 ℃/min. A holding step at 1600 ℃ for 30 min was employed before reaching target temperatures (i.e., 1900-2200 ℃) for 2 h.

The density was measured by the Archimedes method. The phase composition was analyzed by X-ray diffraction (XRD), and the microstructure was characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS). The grain size was determined based on the SEM images, and the electron backscatter diffraction was employed to evaluate the crystallographic orientation and geometrically necessary dislocation density.

(Hf, Zr)B₂ without B₄C addition exhibits a poor sinterability, achieving the relative density of only 57.2% at 1900 ℃. and gradually increasing to merely 88.6% even at 2200 ℃. The addition of B₄C transforms a densification behavior. At 2000 ℃, the sample containing 2% and 5% B₄C achieves the relative densities of 97.8% and 98.1%, respectively, representing an increase of >30% compared to the sample without B₄C (i.e., 74.8% at 2000 ℃). This enhancement is attributed to the effective "deoxidizing" function of B₄C, reacting with and removing surface oxide impurities, thereby activating mass transport mechanisms essential for pore elimination and grain boundary migration. At > 2000 ℃, the relative density decreases slightly for the samples with B₄C. At 2100 ℃, accelerated grain boundary mobility begins to outpace pore migration, leading to the formation of some intragranular pores. At 2200 ℃, the B₄C-(Hf, Zr)B₂ system reaches its eutectic point, triggering liquid-phase sintering as evidenced by B₄C exhibiting melt-like morphology along grain boundaries with good wetting characteristics. The samples with B₄C addition exhibite a significant grain growth at elevated temperatures. For the sample with 2% B₄C, the grain size increases from (4.81 ± 0.99) μm at 2000 ℃ to (45.07 ± 16.20) μm at 2200 ℃, while the sample with 5% B₄C increases from (3.35 ± 0.84) μm to (26.21 ± 7.50) μm. The finer grain in the sample with the more addition of B₄C is attributed to an enhanced pinning effect due to a higher content of secondary phase particles, which effectively inhibits a grain boundary migration. This grain coarsening, accompanied by pore coalescence, contributes to a slight decrease in relative density to 94.5% for the sample with 2% B₄C and 94.6% for the sample with 5% B₄C at 2200 ℃. The EBSD analysis reveals that the geometrically necessary dislocation density decreases at 2200 ℃, compared to the cases at lower sintering temperatures. The Kernel average misorientation mapping shows that the strain concentrations near grain boundaries and B₄C particles are somewhat relieved in liquid-phase sintered samples. This phenomenon is related to the dissolution-reprecipitation mechanism and the presence of the liquid phase during sintering. Although B₄C participates in liquid formation at 2200 ℃, it recrystallizes upon cooling and retains its structure in the final ceramic, indicating a chemical compatibility with the matrix throughout the thermal cycle.

The introduction of B₄C significantly promoted pressureless sintering densification of (Hf, Zr)B₂ ceramics. The samples containing 2% and 5% B₄C achieved the relative densities of 97.8% and 98.1% at 2000 ℃, respectively, which exceeded the sample without B₄C. Sintering temperature critically controlled the microstructural evolution. The dense microstructures with fine grains were obtained at 2000 ℃. At 2100 ℃, accelerated mass transport led to intragranular pores and rapid grain growth during solid-state sintering. At 2200 ℃, liquid-phase formation caused a significant grain coarsening and a slight density decrease, while effectively relieving internal strain, with B₄C recrystallizing upon cooling and retaining its structure. Considering both density and microstructure, the optimal pressureless sintering temperature for (Hf, Zr)B₂ ceramics with B₄C additions could be approximately 2000 ℃, providing a viable process window for (Hf, Zr)B₂-based ultra-high temperature ceramic composites.

Y₃NbO₇-YNbO₄ composite ceramic materials were synthesized by in-situ synthesis and solid-state reaction methods. The effect of YNbO₄ content (i.e., 0 to 70% in volume fraction) on the two-phase structure, distribution, and properties of the composite ceramics were investigated. W The results show that the hardness and strength of the composite ceramics decrease with the increase in YNbO₄ content. At YNbO₄ content of 30%, the composite ceramic can maintain a high Vickers hardness of 8.99 GPa and a strength of 121.89 MPa, while the fracture energy is increased by approximately 18%, showing good comprehensive strength and toughness. Also, YNbO₄ in C1 can be diffusely distributed around Y₃NbO₇, preventing the formation of high thermal conductive pathways. Meanwhile, the interface between the two phases and the refractive index difference enhances the scattering of sound/photons, thereby increasing the infrared radiation emissivity in the range of 2.5-14.0 μm at high temperatures and suppressing an increase in thermal conductivity at high temperatures. At 1000 ℃, the thermal conductivity is only 1.29 W·m^-1·K^-1.

In this study, Y₃NbO₇-YNbO₄ series ceramic materials were prepared by in-situ synthesis and solid-state reaction methods. The phase of Y₃NbO₇-YNbO₄ composite ceramics was characterized by X-ray diffraction (XRD). The microstructure morphology of the ceramic samples was analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The grain size of each sample was statistically analyzed bya software named ImageJ, and the size distribution was fitted by the Gaussian peak. The Vickers hardness (H_V) of the samples was determined by indentation method using a micro-Vickers hardness tester (HVT-1000A), and the indentation and crack were prefabricated. The three-point bending test was carried out on the composite ceramic samples by an electronic universal testing machine to obtain the stress-strain curve and the flexural strength of the material. The thermal diffusivity (α) was measured at 25-1000 ℃ by a laser flash diffusivity analyzer. The infrared emissivity in the range of 2.5-14.0 μm was characterized by Fourier transform infrared spectroscopy (FTIR).

For the mechanical properties, the Vickers hardness (H_V) of the pure phases of Y₃NbO₇ and YNbO₄ are 11.19 GPa and 4.82 GPa, respectively. The hardness of the Y₃NbO₇-YNbO₄ composite ceramics lies between the two pure phases, and its hardness has a good stability due to the uniform dispersion of the two phases in the composite material. At YNbO₄ content of 30%, the fracture surface of the composite ceramics shows a tortuous and undulating feature, accompanied by the pull-out phenomenon of the second phase grains, and the layered fracture morphology within the YNbO₄ grains also occurs. This fracture feature is closely related to the layered ferroelastic domain skeleton structure within the YNbO₄ grains. Under the driving of the stress field at the crack tip, the domain structure can adjust the atomic arrangement and orientation, thereby changing the crack propagation path and ultimately forming a layered fracture morphology. Regarding thermal properties, the thermal conductivity upturn phenomenon of sample C1 is significantly mitigated, and its high-temperature thermal conductivity is lower than that of the pure phase of Y₃NbO₇, with a thermal conductivity of only 1.29 W·m^-1·K^-1 at 1000 ℃. The microstructural analysis indicates that a small amount of YNbO₄ second phase in sample C1 is dispersed around the Y₃NbO₇ grains, and this distribution effectively blocks the formation of high thermal conductivity pathways, resulting in the lowest overall thermal conductivity performance in this series of materials. At the interface between the Y₃NbO₇ and YNbO₄ phases, due to the differences in lattice constants and crystal orientations, more significant lattice distortions occur compared to single-phase grain boundaries, forming strong phonon and photon scattering centers. The Y₃NbO₇-YNbO₄ composite material exhibits superior high-temperature thermal radiation shielding performance due to the high intrinsic emissivity of the YNbO₄ phase and the special optical properties formed after the two-phase composite.

A series of Y₃NbO₇-YNbO₄ composite ceramics with composition gradients were in-situ synthesized. The content and distribution state of the second phase YNbO₄ had a decisive influence on the comprehensive performance of the composite ceramics, especially the composite ceramic with 30% YNbO₄ content (sample C1) showed the optimum comprehensive performance. In terms of mechanical properties, the sample C1 maintained a relatively high bending strength (i.e., 121.89 MPa) and its fracture energy was 18% greater than that of the pure Y₃NbO₇ phase, achieving an optimization of toughness. Regarding thermal insulation performance, the YNbO₄ phase in the sample C1 was dispersed in a spherical form at the grain boundaries of the Y₃NbO₇ phase, and the Y₃NbO₇ phase blocked the interconnection between the YNbO₄ phases. This unique distribution could effectively block the formation of high thermal conductivity pathways. The second phase effectively suppressed the upward trend of the high-temperature thermal conductivity of the Y₃NbO₇ phase. At 1000 ℃, the thermal conductivity was only 1.29 W·m^-1·K^-1, which was 20% lower than that of the pure Y₃NbO₇ phase (i.e., 1.59 W·m^-1·K^-1), significantly reducing the upward trend. This optimization effect could be attributed to the increase in the high-temperature infrared emissivity of the material after the introduction of the YNbO₄ phase, thereby weakening the heat flow transmission dominated by infrared thermal radiation. In summary, the Y₃NbO₇-YNbO₄ composite ceramics achieved the performance synergy of low thermal conductivity and high strength and toughness through reasonable composition design and in-situ synthesis strategy. The sample C1 with excellent comprehensive performance could have a great application potential in the field of high-temperature thermal protection.

This review systematically distills core strategies derived from biomineralization and translates them into material preparation techniques. It becomes increasingly feasible to fabricate macroscopic composites that combine high hardness, strength, and toughness under near-room-temperature conditions via integrating biomineralization strategies such as 'in-situ phase transformation and densification of hydrated precursors' and 'interfacial engineering of hierarchical structures'. This review provides a theoretical foundation and technical basis for the development of green and sustainable routes to high-performance ceramics. However, the existing research still falls short of replicating the exquisite structures and exceptional properties in biological materials and remains distant from practical applications. Future research should focus on the following directions, i.e., 1) gaining a deeper understanding of the biological formation of structural materials, particularly the kinetic principles governing mass transport, reactions, and assembly, to provide theoretical guidance for artificial synthesis; 2) further expanding the applicability of bioprocessing inspired room/low-temperature ceramic densification techniques to a broader range of material systems; 3) introducing advanced technological approaches to reduce the processing scale to the nanometer level, such as in-situ mineralization growth, layer-by-layer hot pressing of nanofilms, and the incorporation of liquid metal ionic bonds; and 4) employing chemical strategies to construct stronger interfacial bonding, thereby enhancing the densification of composites under low-pressure conditions. These efforts will lay a groundwork for the fabrication of large-scale composites at room or low temperatures.

This review summarizes recent progress on the synthesis, mechanisms, and applications of persistent luminescent and mechanoluminescent nanomaterials. We emphasize that advances across both top-down and bottom-up routes substantially improve control over particle size, morphology, and-critically-the defect/trap structures governing carrier trapping and detrapping. We highlight a trap-centric perspective that links delayed emission in persistent luminescence with stress-assisted carrier release in mechanoluminescence via comparing the physical bases of the two phenomena. Translating these materials to the nanoscale can broad their utility, particularly for autofluorescence-free bioimaging and diagnostics, as well as self-powered, visually intuitive stress sensing and flexible optoelectronic devices. Collectively, these studies illustrate a shift from viewing luminescence as an isolated metric toward engineering integrated, stimulus-responsive nano-systems tailored to application demands.

Some key challenges remain despite a rapid development. A central limitation is the trade-off between achieving precise nanoscale structural control and preserving the deep, stable trap populations needed for strong afterglow or mechanoluminescent output. In addition, a predictive and quantitative understanding of how interfaces, surface states, and localized mechanical fields regulate carrier dynamics in nanomaterials is still lacking. For practical deployment, a long-term stability under environmental and cyclic loading, biocompatibility, and scalable yet reproducible fabrication must be addressed. Future work should involve: 1) advancing in-situ/operando characterization and computation to map trap distributions and carrier pathways, 2) developing hybrid or composite architectures that balance structural integrity with optical functionality, and 3) validating application-driven prototypes in realistic settings from deep-tissue theranostics to structural health monitoring.

Although a significant progress is made in the research on material design and luminescent properties of organic-inorganic hybrid Cu-based halides, there are still some issues with organic-inorganic hybrid Cu-based halides that need to be addressed. This review proposes some directions for future in-depth research. First, in future explorations of organic-inorganic hybrid Cu-based halides, it is recommended for high-performance and widely applicable organic-inorganic hybrid Cu-based halides to design structures and synthesize the related materials with specific performance targets. Second, a deeper exploration of the luminescence mechanisms of organic-inorganic hybrid Cu-based halides is needed. Currently, the luminescence mechanisms of organic-inorganic hybrid Cu-based halides are complex and diverse. Previous reports have not clearly clarified the mechanisms of metal-to-organic ligand charge transfer and halogen-to-organic ligand charge transfer luminescence. Future studies can conduct more in-depth discussions in this area. Then, a research on organic-inorganic hybrid Cu-based halide glasses should be increased. These glasses have rich luminescent properties, but the existing research is limited. A future work can enrich studies in the field of organic-inorganic hybrid Cu-based halide glasses. In addition, conventional films of organic-inorganic hybrid Cu-based halides used for X-ray imaging face some problems such as particle aggregation and low transparency, restricting their practical application to some extent. Glass materials with high optical transparency and processability can be made into transparent scintillator materials, which are crucial for achieving high-resolution X-ray imaging. Finally, the applications of organic-inorganic hybrid Cu-based halides should be expanded. Their practical applications should be enriched in fields such as WLEDs, X-ray imaging, near-infrared night vision imaging, and anti-counterfeiting. For white WLEDs and X-ray imaging, exploring the value of practical applications requires the development of novel systems. For near-infrared night vision imaging, there are currently few reports of organic-inorganic hybrid Cu-based halides with near-infrared luminescence. In the future, more near-infrared luminescent materials can be explored to obtain near-infrared night vision imaging materials with the excellent performance.

Multiferroic materials, which exhibit two or more primary iron orders (such as ferroelectricity and ferromagnetism), hold a significant potential in sensing and storage applications. BiFeO₃ stands as the most representative room-temperature single-phase multiferroic material. Its ferroelectricity originates from lattice distortion caused by the 6s² lone-pair electrons of Bi³⁺hybridizing with O 2p, while magnetism arises from Fe—O—Fe super-exchange. However, its narrow bandgap results in high leakage current and coercive field, making ferroelectric characterization challenging. Also, the periodic arrangement of G-type antiferromagnetic structures renders it macroscopically non-magnetic with a weak magnetoelectric coupling. Researchers develop some methods such as ion substitution and process optimization, among which composites with magnetic materials are effective in inducing magnetism and enhancing magnetoelectric coupling. M-type strontium ferrite (i.e., SrFe₁₂O₁₉, abbreviated as SrM) as a typical permanent magnet with high saturation magnetization has attracted attention due to its complex magnetic structure that can induce ferroelectric polarization, but its high leakage current limits its application in electrically controlled magnetism. To address this issue, this study was to introduce SrM into the BiFeO₃ matrix to enhance magnetism and magnetoelectric coupling. To overcome the high leakage current of pure BiFeO₃, we selected 0.75BiFeO₃-0.25BaTiO₃ (BFO-BTO) with superior iron-voltage properties as a ferroelectric matrix.We prepared a series of (1-x)(BFO-BTO)/xSrM composite multiferroic ceramics via solid-state reaction and systematically investigated the evolution of their structural, ferroelectric, magnetic, and magnetoelectric coupling properties.

In this study, (1-x)(BFO-BTO)/xSrM composite ceramics were synthesized by a solid-state reaction method. Bi₂O₃, Fe₂O₃, SrCO₃, BaCO₃, and TiO₂ (all with purity ≥99.9%) were used as raw materials. The materials were weighed in stoichiometric proportions after drying and ground in deionized water for 24 h. The slurries were dried and sieved, then subjected to pre-sintering for BFO-BTO at 870 ℃ for 3 h and SrM at 1100 ℃ for 3 h. The resulting powders were mixed proportionally, ground again for 24 h, dried, granulated, and pressed into green bodies (10 mm diameter, 1-2 mm thickness), followed by sintering at 940 ℃ for 3 h. The sintered samples were polished and coated with silver paste, then fired at 700 ℃ for electrodes.

The crystal structure was analyzed by X-ray diffraction (XRD). The surface morphology was determined by scanning electron microscopy (SEM), and the elemental distribution was analyzed by energy dispersive spectroscopy (EDS). After 30 min polarization in a DC electric field of 40 kV/cm, the samples underwent performance testing. The dielectric properties were obtained by an impedance analyzer with a high-temperature testing system. The room-temperature ferroelectric properties were measured by a ferroelectric analyzer. The room-temperature magnetic properties before and after polarization were determined by a vibrating sample magnetometer (±20 kOe). The linear magnetoelectric coupling coefficient was determined by a magnetoelectric effect measurement system (at a test frequency of 2 kHz, DC bias magnetic fields of 0-3 kOe, and an AC excitation magnetic field of 1.07 Oe. The coupling coefficient was calculated based on α_ME = δV/(δHt).

The structure, electrical, magnetic and magnetoelectric coupling properties of BFO-BTO/SrM composite ceramics are systematically investigated. The XRD patterns indicate that the composite consists of coexisting perovskite-type BFO-BTO and hexagonal SrM phases. The proportion of rhombohedral R3c phase in BFO-BTO gradually increases, while the tetragonal P4mm phase decreases as the SrM content increases, demonstrating that SrM addition affects the phase composition of BFO-BTO. The Rietveld refinement results are in reasonable agreement with the XRD patterns. The backscattered electron imaging reveals that the SrM phase (dark region) is uniformly distributed within the BFO-BTO matrix (bright region), exhibiting a point-like dispersion at a low doping and aggregation at a high doping. The surface scanning confirms a minor interphase element diffusion between the two phases. The average grain size of BFO-BTO increases from 0.80 μm to 1.53 μm with increasing the SrM content. The XPS spectra reveal that Fe in all the samples exists in mixed valence states of Fe²⁺/Fe³⁺, with the valence ratio showing a minimal variation upon SrM addition. The oxygen vacancy concentration has a slight increase as the SrM content increases, remaining in the range of 45%-56%.

The dielectric properties show that the dielectric constant and loss increase gradually with the increase of SrM content, which is attributed to the Maxwell-Wagner interface polarization effect. Two dielectric anomaly peaksappear in the high temperature dielectric spectra at 510 ℃ and 600 ℃, corresponding to the Curie temperature of SrM and the BFO-BTO ferroelectric phase transition temperature, respectively. The ferroelectric measurements demonstrate that a moderate content of SrM (i.e., x=0.015) optimizes the ferroelectric properties, achieving a remanent polarization of 27.33 μC·cm^-2. However, the excessive content of SrM causes a sharp increase in leakage current and ferroelectric deterioration. The PFM analysis confirms that SrM addition weakens the polarization response. The results of magnetic property tests reveal that the magnetization strength of the composite material increases significantly with the increase of SrM content. As x=0.015, the saturation magnetization reaches 4.15 emu·g^-1, which exceeds that of pure BFO-BTO (i.e., 0.4 emu·g^-1). The sample exhibits a pronounced magnetic anisotropy, with a parallel magnetization outperforming perpendicular magnetization. After poling treatment, the remanence of the sample changes markedly, indicating the presence of stress/charge-mediated magnetoelectric coupling. The results of magnetoelectric coupling tests demonstrate that the coupling coefficient exhibits an initial increase and a subsequent decrease with increasing SrM content, reaching a maximum of 0.72 mV·cm^-1·Oe^-1 as x=0.035. An appropriate incorporation of SrM enhances strain-mediated magnetoelectric coupling, whereas the excessive addition degrades the piezoelectric performance and weakens the coupling effect. Compared with the similar studies, this system demonstrates a superior comprehensive performance optimization.

This study prepared (1-x)BFO-BTO/xSrM composite multiferroic ceramics. The results showed that the introduction of SrM could modulate the phase composition, with the optimized ferroelectric performance (i.e., P_r=27.33 μC·cm^-2) as x=0.015and the maximum magnetoelectric coupling coefficient (i.e., 0.72 mV·cm^-1·Oe^-1) as x=0.035. The material could demonstrate potential applications in storage, sensing and related fields.

SiBCN polymer-derived ceramics (PDCs) are highly promising for high-temperature electromagnetic wave attenuation due to their unique "wave-transmitting/lossy" composite structure, which arises from the in-situ formation of high-dielectric crystals within a low-dielectric amorphous matrix. A critical challenge, however, lies in precisely tailoring their microstructure to maximize absorption performance. To address this issue, SiBCN ceramics were synthesized with different compositions via modulating the silicon (Si) content in the polymer precursors to elucidate the regulatory mechanisms governing phase composition, morphology, and electromagnetic absorption properties. The results reveal that high-temperature treatment induces the crystallization of Si₃N₄, SiC, and graphitic carbon. The incorporation of Si can facilitate the graphitization of amorphous carbon and effectively reduce internal defect density. Furthermore, an increase in Si content promotes the formation of the Si₃N₄ phase, thereby enhancing impedance matching. The optimized SiBCN ceramics demonstrate superior microwave absorption capabilities, achieving a minimum reflection loss of -54.38 dB at 13.49 GHz (2.28 mm thickness) and a broad effective absorption bandwidth of 6.61 GHz (2.24 mm thickness). Consequently, this study confirms that tuning the precursor Si content effectively optimizes both the structural configuration and impedance matching of SiBCN ceramics, offering a robust theoretical and experimental foundation for their application in high-temperature environments.

Under ice bath conditions, 20 g of n-hexane was added to a reaction flask, followed by the sequential addition of dimethyldichlorosilane, boron trichloride, borane dimethyl sulfide complex, and hexamethyldisilazane according to different molar ratios of the raw materials. The mixture was stirred in Ar atmosphere for 24 h. The temperature was then raised to 100 ℃ and maintained for 3 h to remove n-hexane and other by-products. Finally, the temperature increased to 160 ℃ and maintained for 3 h, followed by three cycles of vacuum filtration to obtain a pale yellow resin-like polyborosilazane. A series of polyborosilazanes with different silicon contents were prepared via varying the amount of dimethyldichlorosilane added. The samples with different dimethyldichlorosilane to hexamethyldisilazane molar ratios of 1∶6, 2∶6, and 4∶6 were designated as S30, S38, and S45, with silicon contents of 30%, 38%, and 45%, respectively.

The precursor samples (S30, S38, and S45) were first cured under an N₂ atmosphere by heating to 280 ℃ at a rate of 2 ℃/min and holding for 2 h. The cured samples were subsequently heated to 1000 ℃ under an N₂ atmosphere at a rate of 5 ℃/min and held for 1 h. They were then further heated to either 1400 or 1600 ℃ at a rate of 2 ℃/min and held for 2 h. The resulting ceramic samples were designated as S30-1400, S38-1400, S45-1400, S30-1600, S38-1600, and S45-1600, respectively.

The phase composition, microstructure, and electromagnetic properties of the resulting ceramics are regulated via controlling the silicon content in the polymer precursor. The results indicate that after heat treatment in N₂ atmosphere at 1600 ℃, crystals such as Si₃N₄, SiC, and graphitic carbon are formed within the SiBCN ceramics. Silicon promotes the transformation of amorphous carbon into crystalline carbon in the SiBCN ceramics, reduces the defect density within the ceramics, and enhances the graphitization degree. The formation of Si₃N₄ in the SiBCN ceramics increases with increasing silicon content, improving the impedance matching performance of the ceramics. When the thickness of the SiBCN ceramics is 2.28 mm, the minimum reflection loss reaches -54.38 dB at 13.49 GHz. At a thickness of 2.24 mm, the effective absorption bandwidth is 6.61 GHz.

This study systematically investigated the influence of silicon content on the phase composition, microstructure, and electromagnetic wave absorption properties of SiBCN ceramics, and thoroughly elucidated the underlying absorption mechanisms.

The results demonstrated that after heat treatment at 1600 ℃, the polyborosilazane precursor transformed into a ceramic matrix containing crystalline phases such as Si₃N₄, SiC, and graphitic carbon. The formation of Si₃N₄ and SiC crystals significantly increased with increasing silicon content, effectively optimizing the impedance matching characteristics of the ceramics. Concurrently, the graphitization degree of amorphous carbon increased, while the defect density within the ceramic decreased. The formation of numerous nano-sized dielectric grains and heterogeneous interfaces markedly enhanced the electromagnetic wave absorption capacity via strengthening interfacial polarization and conductive loss.

The experimental results indicated that the sample with 38 wt.% silicon content exhibited the optimal comprehensive wave absorption performance: at a thickness of 2.28 mm, the minimum reflection loss (RLmin) reached -54.38 dB at 13.49 GHz. At a thickness of 2.24 mm, the effective absorption bandwidth (EAB) extended to 6.61 GHz. Therefore, the microstructure and phase composition of the ceramics could be effectively regulated via adjusting the silicon content in the precursor, leading to the development of SiBCN ceramic materials with excellent electromagnetic wave absorption properties.

Carbon-ceramic composite materials, which seamlessly integrate the exceptional mechanical strength, high-temperature tolerance, corrosion resistance, and thermal shock resistance of ceramics with the superior electrical conductivity of carbon-based materials, exhibit an immense application potential in various fields. They are particularly critical in the manufacturing of closing resistors for ultra-high voltage (UHV) circuit breakers. Under extreme service environments characterized by high temperatures, high pressures, intense electromagnetic fields, and the corrosive byproducts of SF₆ decomposition, these key components face stringent performance requirements, including high mechanical strength, controllable and stable resistivity, a low temperature coefficient of resistance (TCR), and remarkable thermal shock resistance. Conventional conductive ceramics predominantly utilize nano-carbon fillers such as carbon black, carbon nanotubes, carbon fibers, and graphene. However, these nano-sized carbon materials typically suffer from severe agglomeration, poor interfacial wettability with the ceramic matrix, and high susceptibility to oxidation during the high-temperature sintering process, severely limiting their structural integrity and functional stability. To overcome these bottlenecks, this study was to introduce a pre-synthesized carbon nanofiber/calcium aluminate composite powder (CNFs/CAC) as an innovative conductive filler. The implementation of CNFs/CAC could effectively mitigate the agglomeration of nano-sized carbons. Furthermore, the unique microstructural architecture of CNFs/CAC could facilitate the construction of a robust three-dimensional carbon conductive network and leverage calcium aluminate as an efficient sintering aid to promote particle rearrangement and matrix densification, thereby lowering the required sintering temperature. Crucially, the CAC shell encapsulating the carbon nanofibers significantly retarded their oxidation at elevated temperatures. Sintering temperature acts as a paramount thermodynamic variable governing densification kinetics, phase transformations, and microstructural evolution. Inadequate temperatures fail to provide a sufficient driving force for grain boundary migration, resulting in excessive porosity and deteriorated mechanical properties. Conversely, excessive temperatures provoke abnormal grain growth, disruption of the percolation network, and pronounced oxidation of the carbon phase. Therefore, this study was to investigate the evolution mechanisms of phase composition, microstructure, mechanical strength, and electrical properties of CNF/ceramic composites at a sintering temperature range of 1300-1500 ℃, to optimize processing parameters and provide a robust theoretical foundation for the fabrication of high-performance composite conductive ceramics.

The ceramic matrix raw materials comprised bauxite, kaolin, and potassium feldspar, while the conductive filler was a laboratory-synthesized CNFs/CAC powder. The introduction of CaO via the CAC into the Al₂O₃-SiO₂ system deliberately promoted the formation of anorthite, subsequently generating a liquid phase that substantially enhanced the liquid-phase sintering process. The preparation commenced with mixing the raw materials (i.e., 60% bauxite, 22% kaolin, 18% potassium feldspar, and 1.5% CNFs/CAC) by dry ball milling in a ball-to-material mass ratio of 2∶1 at 320 r/min for 9 h. The homogeneous mixture was then granulated through a 20-mesh sieve to obtain granules of approximately 0.85 mm in diameter. These granules were uniaxially pressed into cylindrical green bodies (20 mm in diameter and 20 mm in height) at 50 MPa, followed by cold isostatic pressing (CIP) at 200 MPa for 300 s to ensure initial uniformity. The compacts were dried at 300 ℃ for 2 h and subsequently sintered in a carbon-embedded graphite crucible atmosphere. The sintering profile was systematically varied from 1300 ℃ to 1500 ℃. The phase compositions were analyzed by X-ray diffraction (XRD), and microstructural morphology alongside elemental carbon distribution was determined by field emission scanning electron microscopy (FESEM) with energy dispersive spectrometry (EDS). The macroscopic physical properties, including apparent porosity and bulk density, were measured by the Archimedes method. The compressive strength was tested by a universal testing machine, while the volume resistivity and TCR were evaluated by a precise digital LCR meter coupled with a controlled electro-thermal drying oven.

The sintering temperature fundamentally dictates the structural evolution and functional performance of carbon nanofiber/ceramic composite resistive materials at 1300-1500 ℃. Elevated temperatures facilitate a liquid-phase formation, drastically reducing apparent porosity from 31% to 23% and boosting bulk density from 2.11 g/cm³ to 2.31 g/cm³. Nevertheless, exceeding 1400 ℃ exacerbates carbon depletion via the Boudouard reaction, irreversibly disrupting the conductive pathways and spiking resistivity. The material achieves its optimal comprehensive properties precisely at 1400 ℃, yielding a compressive strength of 189 MPa, a minimal resistivity of 476 Ω·cm, a highly stable NTC behavior with a TCR of -0.14%/℃, and a lowest I_D/I_G ratio of 0.85, reflecting an exceptional graphitic ordering. The incorporation of the pre-synthesized CNFs/CAC filler serves a dual purpose. It establishes a highly uniform and continuous conductive percolating network at minimal doping levels, and it synergistically has fracture toughness via inducing sophisticated crack deflection and bridging mechanisms, offering a robust paradigm for advanced composite electro-ceramics.

Lutetium oxide (Lu₂O₃) transparent ceramics have a great potential in high-power or high-efficiency solid-state laser applications due to the excellent thermal-mechanical properties, low fabrication temperature, high absorption and emission cross-sections when doped with trivalent rare earth laser ions. Among them, Lu₂O₃ doped with Yb³⁺ stands out as the best combination for applications in high-efficiency and high-power lasers, considering a high thermal conductivity due to the similar ionic radii and bonding forces of lutetium and ytterbium ions. The combination of vacuum pre-sintering with HIP post-treatment, along with the powder synthesized by a co-precipitation method, highly favors to fabricate highly transparent sesquioxide ceramics. Some previous reports demonstrated the high efficiency and high power laser outputs of Yb:Lu₂O₃ transparent ceramics. Thermal properties of Yb:Lu₂O₃ ceramics are significant for the high-efficiency and high-power laser applications. In ceramic gain media, the significant factors affecting the thermal conductivity include the doping content of active ions, porosity and grain size. Although increasing Yb³⁺ concentration could not cause a decrease in thermal conductivity in theory, little work has reported the related experimental investigations yet.

The commercial oxide powders (i.e., Lu₂O₃ and Yb₂O₃) were utilized as raw materials. Ammonium bicarbonate (NH₄HCO₃) and ammonium sulfate ((NH₄)₂SO₄) were used as a precipitant and a dispersant, respectively. The precursors of Yb:Lu₂O₃ were synthesized by a co-precipitation method. All the precursors with different Yb³⁺ doping contents were calcined at 1050 ℃ to obtain Yb:Lu₂O₃ powders, which were dry-pressed at a low pressure in a steel die and then cold-isostatically pressed at 250 MPa. All the green bodies were vacuum sintered at 1500 ℃ for 2 h to fabricate pre-sintered ceramics that then were HIP post-treated in Ar atmosphere pressure of 176 MPa at 1750 ℃ for 3 h. Finally, the HIP post-treated ceramics were annealed in air at 900 ℃ for 10 h and then polished on the both sides to a thickness of 1.3 mm for the coming optical characterizations. Some annealed transparent ceramic disks were then machined to the sizes of (Φ = 10.0 mm, d = 1.3 mm) and (Φ=5.5 mm, d<1.0 mm) for measuring the thermal diffusivity and specific heat, respectively.

The phase compositions of the synthesized precursors and powders were identified by X-ray diffraction (XRD, Cu Kα1 radiation, λ = 0.154 18 nm). The microstructures of all the powders and ceramics were determined by field emission scanning electron microscopy (FESEM, SU8220, Hitachi, Japan). The in-line transmittance and absorption spectra of Yb∶Lu₂O₃ transparent ceramics were characterized by ultraviolet-visible-near infrared spectroscopy (UV-VIS-NIR, Carry-5000, Varian, USA). The thermal diffusivity was measured by a laser-flash method, and the specific heat was measured by differential scanning calorimetry (DSC).

Pure Lu₂O₃ precursor consists of spherical particles with various sizes, which range from tens of nanometers to hundreds of nanometers in diameter, but the micro-morphology of the precursor with Yb³⁺ is made of thin stacked layers with nano-sized thickness, indicating that Yb³⁺ doping has a great impact on the morphologies of Lu₂O₃ precursor, but its concentration level does not affect the morphologies of the precursors apparently. The particles of Yb³⁺-doped nano-powders agglomerate in two-dimensional space and are in the shape of regular polyhedra. The phases of all the calcined nano-powders are consistent with those of cubic Lu₂O₃. The lattice parameters of Yb:Lu₂O₃ nano-powders are 10.384 4、10.389 4、10.390 2、10.394 9 Åand 10.396 5 Å, respectively, with increasing the Yb³⁺ concentration. The corresponding average gain sizes are 57.7, 51.9, 53.6, 61.8 and 51.4 nm, respectively. The relative densities of all the Yb:Lu₂O₃ pre-sintered ceramics are 95.3%, 96.1%, 95.6%, 95.4% and 95.7%, with average grain sizes of 0.92, 0.97, 0.99, 1.09 μm and 1.14 μm, respectively, as Yb³⁺ concentration increases. 3% Yb:Lu₂O₃ transparent ceramic sample has the maximum in-line transmittance with the values of 83.0% at 1080 nm and 78.8% at 600 nm. The absorption coefficients at 948 nm of these ceramics are linearly correlated to Yb³⁺ doping content, which follows the Lambert-Beer Law. Four main emission peaks are located at 948, 976, 1033 and 1079 nm, respectively, among which the largest emission cross-section is at 976 nm with a value of 1.148×10^-20 cm². The laser emission wavelengths include 1079 nm and 1033 nm. The maximum thermal conductivity of 3% Yb∶Lu₂O₃ ceramics is 13.1 W·m^-1·K^-1 at room temperature, which is similar to the value of Yb:Lu₂O₃ single crystal, while the thermal conductivity of 15% Yb∶Lu₂O₃ ceramics is 11.6 W·m^-1·K^-1, which is greater than that of pure YAG material. The result indicates that Yb:Lu₂O₃ transparent ceramics are a gain medium with a high thermal conductivity, even doped with a high Yb³⁺ doping content, demonstrating a great application potential in high-power solid-state lasers.

Yb:Lu₂O₃ transparent ceramics with Yb³⁺ doping content of 0-15% were fabricated by vacuum sintering and HIP post-treating from co-precipitated nano-powders. The nano-powders calcined at 1050 ℃ had the similar particle sizes with different morphologies as the precursors. 3% Yb∶Lu₂O₃ nano-powder showed a better dispersivity, and the corresponding transparent ceramics possessed the maximum optical quality with the in-line transmittance of 83% at 1080 nm. The spectral characteristics of all the Yb:Lu₂O₃ transparent ceramics were calculated. At β of > 0.059, there were two main lasing emission wavelengths, peaked at 1033 nm and 1079 nm, respectively. 3% Yb:Lu₂O₃ transparent ceramics possessed better thermal properties rather than others, with the room-temperature thermal conductivity of 13.1 W·m^-1·K^-1. The results indicated a great application potential of Yb:Lu₂O₃ transparent ceramics in high-power solid-state lasers.

The rapid advancement of new energy technologies such as photovoltaics, hydrogen energy, and electric vehicles has stringent demands on the heat dissipation capacity of high-power devices. Silicon nitride (Si₃N₄) ceramics with a high thermal conductivity are considered as an ideal substrate candidate for packaging applications, due to their excellent thermal and mechanical properties. However, the actual thermal conductivity remains far below its intrinsic value, primarily due to lattice oxygen impurities and various microstructural defects. The sintered reaction-bonded silicon nitride (SRBSN) process has attracted much attention due to its ability to effectively control lattice oxygen, tailor the microstructure, and its low cost. Sintering aids, particularly rare-earth oxide (RE₂O₃), play a key role in determining the final properties. RE₂O₃ contributes to liquid phase sintering and densification and acts as "oxygen scavengers," effectively purifying the Si₃N₄ lattice. Previous studies showed that the type of RE₂O₃ could significantly affect grain morphology, grain boundary characteristics, thereby affecting the thermal conductivity and mechanical properties. Nevertheless, the specific role and underlying mechanisms of RE₂O₃ in the SRBSN process have yet to be systematically elucidated. This work employed MgO-RE₂O₃ as sintering aids to fabricate Si₃N₄ ceramics via the SRBSN process, and systematically investigated the effect of RE₂O₃ type on the nitridation behavior, microstructural evolution, and final properties of the ceramics.

Commercial silicon powder was used as a raw material, with nine different commercial RE₂O₃ and MgO employed as sintering additives. The total amount of sintering aids was fixed at 2.4% RE₂O₃ and 6.8% MgO for all the samples. The raw materials mixed with alcohol as a solvent were ground in a planetary ball mill with Si₃N₄ balls as grinding media for 3 h. The resulting slurry was dried, uniaxially pressed, and then further cold isostatic pressed at 200 MPa to form green bodies. The green bodies were placed in a BN crucible filled with a 1∶1 (by mass) mixture of BN and Si₃N₄ powder. The nitridation and subsequent sintering processes both were conducted in a gas pressure sintering furnace (ZYS-3050, Hunan Jinteke Technology Co., Ltd., China) under a 2 MPa N₂. The thermal schedule consisted of a nitridation step held at 1350 ℃ for 3 h, followed by a sintering step at 1860 ℃ for 12 h. Some samples were cooled to 1600 ℃ for an additional heat treatment duration of 8 h.

The bulk density was measured by Archimedes' method. The theoretical density was calculated according to the rule of mixtures, and the relative density was determined as a ratio of the bulk density to the theoretical density. The phase composition was characterized by X-ray diffraction (XRD). The microstructure of plasma-etched surfaces was determined by field-emission scanning electron microscopy (FESEM). The thermal diffusivity (α) was measured by a laser flash method on the samples with dimensions of 2 mm × 10 mm × 10 mm. The thermal conductivity (κ) was calculated according to the formula κ = ρ · Cp · α, where a fixed specific heat capacity (C_p) value of 0.68 J·g^-1·K^-1 was used. The flexural strength was tested by a three-point bending method, and the fracture toughness of the bar specimens with dimensions of 3 mm × 4 mm × 36 mm was evaluated by a single-edge notched beam (SENB) method.

The XRD patterns reveal that the w(β)/w(α+β) in nitrided bodies displays a U-shaped profile as the RE³⁺ionic radius increases, primarily due to the synergistic regulatory effect of the interfacial reaction activation energy and the liquid phase viscosity on the phase transformation kinetics. After sintering at 1860 ℃, all the samples (except SSN-Eu) achieve densification. The grain size first decreases and then slightly increases with increasing RE³⁺ ionic radius, as a phenomenon primarily regulated by the differential binding energy (δ) and the content of β-Si₃N₄ in the nitrided bodies. RE³⁺ with δ > 0 (e.g., Lu³⁺, Yb³⁺) can enrich in the liquid phase, promoting diffusion-controlled grain growth, while those RE³⁺ with δ < 0 (e.g., La³⁺, Sm³⁺) can segregate on the surfaces of Si₃N₄ particles, suppressing the grain growth. Meanwhile, the β-Si₃N₄ content in the nitride bodies affects both dissolution-precipitation and Ostwald ripening process. These two factors synergistically lead to the variation in grain size. The flexural strength generally exhibits an initial increase and a subsequent decrease with increasing RE³⁺ ionic radius, reaching the maximum value of (908 ± 35) MPa in the SSN-Gd sample. The increase in strength is attributed to the grain refinement, while the subsequent decrease is due to the thermal expansion mismatch between the Si₃N₄ grains and the intergranular phase. After heat treatment at 1600 ℃, the samples SSN-Lu, SSN-Er, and SSN-Y show an improved flexural strength, whereas the properties of the samples SSN-Nd and SSN-La decrease. The fracture toughness decreases with increasing RE³⁺ ion radius, primarily due to the reduced grain size and grain boundary strength. Among the samples, the sample SSN-Yb exhibits the maximum toughness of (8.7 ±0.3) MPa·m^1/2. After heat treatment, the fracture toughness of most samples further enhances, while it decreases in the samples SSN-Sm, SSN-Nd, and SSN-La. The thermal conductivity generally declines with increasing RE³⁺ ion radius, and the thermal conductivity of SSN-Yb reaches 101.2 W·m^-1·K^-1. Heat treatment promotes grain coarsening in most samples, leading to an increase in thermal conductivity, such as 105.6 W·m^-1·K^-1 for the sample SSN-Yb. However, the thermal conductivity of the samples SSN-Nd and SSN-La decreases instead.

The effect of RE₂O₃ (i.e., RE = Lu, Yb, Er, Y, Gd, Eu, Sm, Nd, La) on the microstructure evolution and properties of Si₃N₄ ceramics prepared by the SRBSN process was systematically investigated. The results indicated that RE³⁺ with smaller ionic radius (such as Lu³⁺, Yb³⁺, and Er³⁺) could effectively promote the growth of β-Si₃N₄ grains, forming a microstructure composed of large-sized grains with high aspect ratios, thereby significantly enhancing thermal conductivity. In contrast, RE³⁺ with larger ionic radius (such as La³⁺ and Sm³⁺) suppressed grain growth, favoring the formation of a fine-grained structure. The flexural strength exhibited an initial increase and a subsequent decrease with increasing RE³⁺ ionic radius, reaching the maximum value of (908 ± 35) MPa in the sample SSN-Gd. The thermal conductivity and fracture toughness both could exhibit a general decreasing trend with increasing RE³⁺ ionic radius. The sample SSN-Yb demonstrated the most favorable combination, with a thermal conductivity of 101.2 W·m^-1·K^-1 and a fracture toughness of (8.7 ± 0.3) MPa·m^1/2. After heat treatment at 1600 ℃, a further grain coarsening led to an improvement in thermal conductivity for the most samples. Among them, the sample SSN-Yb could achieve the maximum thermal conductivity of 105.6 W·m^-1·K^-1, while the flexural strength of the samples SSN-Lu, SSN-Er, and SSN-Y also improve. In contrast, the thermal conductivity and flexural strength of the samples SSN-Nd and SSN-La both decreased.

With the rapid development of new thermal management materials, a demand for high quality AlN powders becomes increasingly urgent. The liquid phase precursor method is regarded as a crucial approach for producing high purity AlN nano-powder due to its advantage of homogeneous mixing in molecular level. Therefore, a study on the liquid phase precursor method and the effect of additives within the system on the precursor pyrolysis, liquid phase regulation, and nitridation kinetics is essential for improving the purity, reaction efficiency, and structural uniformity of sized AlN nano-powder. In this study, AlN nano-powder was synthesized by a liquid phase precursor method at low temperatures, and the role, reaction pathways, and regulatory mechanisms of yttrium additives in the precursor system were systematically investigated. This work could provide significant insights toward enhancing powder purity, achieving controlled crystal growth, and optimizing structural homogeneity.

Aluminum chloride hexahydrate was used as an aluminum source and dicyandiamide and melamine as nitrogen sources. Yttrium acetate tetrahydrate acted as a soluble yttrium additive, and methanol was selected as a solvent. The aluminum and nitrogen sources were dissolved in methanol at an N/Al molar ratio of 4, and yttrium was added at 0-3% (calculated as Y₂O₃ in the final AlN). After magnetic stirring for 30 min, a uniform precursor solution was obtained. The solution was dried at 85 ℃ for 12 h, and then ground into a white precursor powder. The precursor powders were placed in covered alumina crucibles and heated in a tube furnace under flowing N₂ to 1100 ℃ at 10 ℃/min, followed by a 3h dwell, to synthesize AlN powders with different yttrium contents. The thermal behavior of yttrium acetate and precursor powders was determined in N₂ by thermogravimetric analysis-differential scanning calorimetry (TG-DSC) from room temperature to 1200 ℃. The phase compositions were examined by X-ray diffraction (XRD, Cu K_α, 20°-80°). The particle morphology of the synthesized powder was determined by field-emission scanning electron microscopy, using an accelerating voltage of 20 kV. The microstructure of the particles in the powder was analyzed by transmission electron microscopy (TEM). The elemental composition and distribution were characterized by energy dispersive spectroscopy (EDS), while the crystalline phase and crystal structure were determined by selected area electron diffraction (SAED).

The liquid phase dispersion combined with a low temperature calcination effectively reduces the synthesis temperature. Compared with the conventional carbothermal reduction method, the Al—Cl bond exhibits a bond strength of approximately 174 kJ/mol, which is lower than that of the Al—O bond, resulting in a reduced activation energy for the reaction. As high nitrogen solid molecules, cyanamide species can release high concentrations of highly reactive nitrogen in-situ on the surface and inside the aluminum precursor, facilitating the completion of the nitridation reaction at a lower temperature for a shorter time. The aluminum source, nitrogen sources, and yttrium additives are mixed and contacted more uniformly due to the excellent dispersibility of the liquid phase, thereby further enhancing both the nitridation rate and its uniformity. The results indicate that the introduction of a small amount of yttrium additive promotes the refinement and uniformity of AlN particles. As the yttrium content increases from 0% to 3%, the AlN particles gradually evolve toward a quasi-spherical morphology, accompanied by improved sphericity and reduced particle size. The average AlN grain size decreases from 74 nm without yttrium addition to 40 nm at 3% yttrium addition. A similar grain-size reduction trend is also obtained based on calculations using the Scherrer equation from the XRD results. The added yttrium additive is uniformly distributed throughout the AlN samples and does not compromise the lattice purity of AlN. No lattice expansion associated with impurity incorporation or solid solution formation occurrs in either the lattice parameters or interplanar spacings.

At the synthesis temperature of 1100 ℃ that could be lower than that required for the carbothermal reduction method, the precursor effectively transformed into crystalline AlN regardless of whether yttrium additives introduced. The addition of a small amount of yttrium effectively promoted the refinement and uniformity of AlN particles, resulting in synthesized AlN powders with relatively uniform particle size and morphology. Yttrium containing compounds had an inhibitory effect on the AlN grain growth, leading to a further refinement of AlN grains in nanoscale. The average grain size of AlN decreased from 74 nm without yttrium addition to 62 nm at 1% yttrium content, and further to 40 nm at 3% yttrium content. The incorporation of yttrium additives did not compromise the lattice purity of AlN during synthesis. The interplanar spacing of AlN nanocrystals remained consistently at 0.270 nm at all yttrium concentrations, corresponding to the plane (100) of hexagonal AlN. In addition, no significant increase occurred in the a-axis, c-axis, c/a ratio, or unit cell volume of AlN nanocrystals with different yttrium contents, confirming the absence of lattice expansion due to the impurity incorporation or the solid-solution formation.

Titanium alloys are particularly well-suited for the fabrication of high-temperature components in aero-engines due to their low density, high specific strength, and excellent oxidation resistance and fatigue performance. However, the difficulty in sintering and insufficient high-temperature performance of Y₂O₃ ceramic cores are the main problems to restrict their application because of the high chemical activity of titanium. At present, the addition of mineralizers can reduce the sintering temperature to a certain extent. However, this reduction in temperature inevitably results in a decrease in porosity, thereby affecting the leachability of Y₂O₃ ceramic cores. To satisfy the criteria associated with investment casting, a dual-mineralizer system can be added to improve the porosity and sintering performance of Y₂O₃. This study was to investigate the synergistic strengthening mechanism of Y₂O₃-based ceramic cores modified with Al₂O₃ and TiO₂ as dual mineralizers.

Y₂O₃ powders with different particle sizes were used as a matrix material, and nano-sized alumina (Al₂O₃) and titanium dioxide (TiO₂) were used as mineralizers. Y₂O₃ ceramic cores with different mixed mineralizer ratios were prepared by a hot-press injection molding method. Key performance parameters of each core sample were obtained based on the aviation industry standard HB 5353. The fracture morphology and element distribution of the cores were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), so as to investigate the synergistic strengthening mechanism of the Y₂O₃-based ceramic cores modified by the dual mineralizers. Meanwhile, a pouring verification was conducted on each ceramic core sample, including wax pressing fracture, the ceramic/metal interface reaction in the alloy after pouring, and the surface quality of the castings.

The sintering process is typically categorized into three distinct stages. The early stage of sintering is marked by the occurrence of bond merging and rearrangement, as well as the predominance of point contact between particles. The middle stage of sintering is marked by the transition from point contact to face contact between the particles and the pores. This progression leads to a further narrowing of the contact area, while maintaining the connection of pores with the surroundings. The late sintering stage is characterized by persistent mass transfer, grain growth, and the pores changing to closed pores, culminating in increased density. The resulting Al₂Y₄O₉(YAM) phase exerts a partial inhibition effect on the particle interface migration during the late-stage sintering process due to the incorporation of Al₂O₃ into Y₂O₃. However, a minimal shrinkage alteration occurs under these dual counteracting mechanisms due to the nano-sizes of Al₂O₃ particles. The incorporation of TiO₂ into Y₂O₃ during the middle stage of sintering results in a significant enhancement of the rate of TiO₂ diffusion into Y₂O₃. This is attributed to the continuous promotion of the mass transfer process by the point defects generated during this stage. The degree of densification exhibits a substantial increase from the middle stage of sintering to the late stage of sintering, accompanied by an increase in the strength of the sample.

In addition, no obvious oxide layer or phase transformation appears in the titanium alloy cast for the sample A3T0.5. The X-ray diffraction (XRD) patterns demonstrate that the titanium alloy is composed of α-Ti and β-Ti phases-phases typically formed during the cooling process of TC4 castings. No characteristic peaks associated with residual Y₂O₃ or interfacial reaction products occur in the XRD patterns. The cross-sectional and internal compositions of the titanium alloy remain pure, without any signs of element infiltration from the ceramic core. This can be attributed to two critical factors, i.e., the Y₂O₃ ceramic core modified by dual mineralizers exhibits a high sintering density, efficiently suppressing the diffusion of core-derived elements into the molten alloy; and Y₂O₃ inherently possesses exceptional chemical inertness, resulting in a weak chemical reactivity with titanium alloy even under the elevated temperatures encounters during casting. Consequently, the inner cavity surface of the as-cast titanium alloy attains favorable quality, fully complying with the service requirements for aerospace castings.

Al₂O₃ reacted with Y₂O₃ to form YAM phase with a better high temperature performance, and formed a looser network structure as Al₂O₃ and TiO₂ contents increased. The addition of TiO₂ could promote the mass transfer process between Al₂O₃ and Y₂O₃, a stable network structure that resisted the sintering shrinkage of Y₂O₃, achieving sufficient high-temperature performance and porosity. The optimal composition of the Y₂O₃ ceramic cores obtained was the addition of 3% of nano-sized Al₂O₃ and 0.5% of nano-sized TiO₂. The shrinkage of the ceramic cores in the length, width, and height directions was 1.86%, 2.33%, and 2.27%, respectively. The high- and room-temperature flexural strengths were 26.09 MPa and 24.25 MPa, respectively. The deflection was 0.158 mm, and the open porosity was 37.1%. Titanium alloy castings of the sample A3T0.5 exhibited a surface roughness of < 2 μm within the inner cavity. These castings could lack a distinct hardening layer as well as the limited penetration of elements from the ceramic matrix into the titanium alloy surface. This could meet a demand for Y₂O₃ ceramic cores in titanium alloy casting for the production of qualified titanium alloy castings.

Alumina (Al₂O₃) ceramics are widely used in high-tech fields such as aerospace, energy, and electronics due to their excellent properties including high hardness, good wear resistance, high temperature stability, and chemical inertness. However, their intrinsic brittleness and high sensitivity to microdefects severely restricttheir practical application in advanced structural components. As a microcrack appears in conventional Al₂O₃ ceramics under an external load, a sudden catastrophic failure is likely to occur, greatly reducing the structural reliability and service life of the material. Therefore, developing a strategy that can effectively improve the toughness and damage tolerance of Al₂O₃ ceramics, while maintaining their inherent excellent properties becomes an urgent and important research topic in the field of structural ceramics. This work was to solve the intrinsic brittleness problem of Al₂O₃ ceramics via combining a structure design with a multi-scale interface regulation, which could be of great significance for promoting the design, development and practical application of high-performance Al₂O₃-based ceramics.

This study proposed an innovative strategy combining a structure design with a multi-scale interface regulation. Al₂O₃/h-BN/Al₂O₃ composite ceramic material with a fine three-dimensional structure and optimized interface properties was constructed through DLP-3D printing technology. The fracture toughness, damage tolerance and energy dissipation capacity of the composite ceramics were significantly improved via skillfully coordinating macro structural design (Gyroid structure) and micro interface modification (h-BN weak interface phase). The following procedure adopted was described. First, the Gyroid structure design was carried out for the Al₂O₃ phase to construct a continuous and stable three-dimensional structural skeleton based on the Digital Light Processing (DLP) 3D printing technology. DLP-3D printing technology was selected due to its advantages of high forming precision, fast printing speed, and ability to fabricate complex three-dimensional structures, which could accurately replicate the designed Gyroid structure and lay a foundation for the structural regulation of composite ceramics. Then, two-dimensional hexagonal boron nitride (h-BN) was introduced as a weak interface phase to regulate the interface properties between the Al₂O₃ structural skeleton and the Al₂O₃ filling phase, thereby constructing the Al₂O₃/h-BN/Al₂O₃ composite ceramic material. A series of composite ceramic samples with different h-BN interface phase contents were prepared to systematically investigate the influence of h-BN content on the material properties. Subsequently, various characterization techniques were used to characterize the phase composition, microstructure and forming quality of the composite ceramics. The mechanical properties such as fracture toughness (K_IC), fracture work, damage tolerance parameters, critical crack size and stress-strain behavior were comprehensively analyzed. Finally, the synergistic effect mechanism of the Gyroid structure and the two-dimensional h-BN weak interface phase on the toughening behavior, damage tolerance and energy dissipation of the composite ceramics was revealed through the analysis of fracture morphology and the summary of performance test results.

The Gyroid-Al₂O₃ ceramic skeleton prepared by DLP-3D printing technology has a good forming quality, and the actual volume fraction of the printed Al₂O₃ structure is 32.6%, which is close to the design value. This indicates that the DLP technology has a high precision in preparing the Gyroid structure, and there is still a certain regulation space to further optimize the printing precision of the structure. In addition, all composite ceramic samples also have a high relative density, which ensures the basic mechanical properties of the material. The composite ceramic with 15% h-BN interface phase (sample A15) shows the optimal comprehensive mechanical properties. Its fracture toughness (K_IC) reaches 5.42 MPa·m^1/2, which is 37% higher than that of pure Al₂O₃ ceramic, the fracture work is 264 J·m^-2, which is nearly 4 times higher than that of pure Al₂O₃, and the maximum fracture toughness (K_JC) can reach 15.40 MPa·m^1/2, which is 290% higher than that of pure Al₂O₃. Also, the critical crack size and damage tolerance parameter of the A15 sample are (201±20) μm and (0.77±0.01) m^1/2, respectively, which are 8.5 times and 2 times higher than those of pure Al₂O₃. Compared with conventional 3D printed ceramics and Al₂O₃ ceramics under conventional toughening strategies, the sample A15 still has significant advantages. The stress-strain behavior of the composite ceramics shows typical progressive failure characteristics and high energy absorption capacity, as well as a typical rising R-curve feature, indicating that the composite ceramics have a strong crack growth resistance and can effectively dissipate energy during the fracture process. The key innovation of this study is that the synergistic effect of the Gyroid structure and the two-dimensional h-BN weak interface phase effectively activates multiple toughening mechanisms such as crack deflection, crack branching, and interface delamination, which breaks through the inherent defect that conventional Al₂O₃ ceramics are extremely sensitive to microdefects, and significantly improves the energy dissipation capacity and structural reliability of the material. This material-structure integration design strategy provides an idea and theoretical guidance for the design and preparation of high-toughness and damage-tolerant composite ceramics.

This work constructed Al₂O₃/h-BN/Al₂O₃ composite ceramic materials with both high toughness and high damage tolerance. The composite ceramics showed progressive failure characteristics and high energy absorption capacity in the stress-strain behaviorand typical rising R-curve characteristics. The fracture toughness was increased by 37% and the fracture work was increased by nearly 4 times, compared with that of pure Al₂O₃. In addition, the critical crack size and damage tolerance parameters of the composite ceramics could also reach (201±20) μm and (0.77±0.01) m^1/2, which were enhanced by 8.5 and 2 times, respectively, compared with those of pure Al₂O₃. This could be due to the synergistic effect of the Gyroid structure and the two dimensional h-BN weak interface phase effectively activating multiple toughening mechanisms such as crack deflection, crack branching, and interface delamination, which could break through the inherent defect that conventional Al₂O₃ ceramics were extremely sensitive to microdefects, and significantly improve the energy dissipation capacity and structural reliability of the material. This material-structure integration design strategy could provide an idea and theoretical guidance for the design and preparation of high toughness and damage-tolerant composite ceramics.

Additive Manufacturing (AM), also known as 3D printing, is widely used due to its advantages such as high design freedom, no need for molds, mass customization, and the ability to construct complex shaped components. The existing 3D printing methods are developed, among which DLP technology has the advantages of fast printing speed, high dimensional accuracy, no need for molds, close to net shape, and high mechanical performance. Ceramic materials are widely used as high-temperature structural functional materials due to their high temperature resistance, oxidation resistance, corrosion resistance, and mechanical properties. However, compared with metal and polymer materials, ceramic materials are still immature in 3D print processing, facing some problems such as limited availability of suitable raw materials, difficulty in optimizing ratios, high costs, poor process stability, and limited mechanical properties. To overcome the problems above, combining photopolymerization 3D printing with ceramic sintering technology becomes an effective method. In this study, ceramic powder and photosensitive preceramic were ground to obtain a uniform slurry with a good flowability, and then high-precision green bodies were formed through DLP.

Polysilazane PSZ-ViH containing both vinyl and Si-H was prepared via ammonified of trimethylchlorosilane, methyltrichlorosilane, methylvinyldichlorosilane, and methylhydrogendichlorosilane. Referring to the reaction conditions above, a Vi-terminated/Si-H containing polysilazane PSZ-TViH was obtained with dimethylvinylchlorosilane, methyltrichlorosilane, and methyldichlorosilane as raw materials. Si-H containing polysilazane LSZ-H was obtained with trimethylchlorosilane, methyltrichlorosilane, and methyldichlorosilane as raw materials. When 2-isocyanatoethyl acrylate (ICA) was used as a modifier, the reaction occurred under stirring in dark conditions at room temperature for 24 h. 2,4,6-trimethylbenzoyl phenyl phosphonic acid ethyl ester (TPO-L) was added as a photosensitizer and stirred in dark conditions for 10 min. PSZ-ViH and Si₃N₄ powders with different mass fractions were ground, ICA and TMPTA were added, and then followed by TPO-L. Finally, a photosensitive polysilazane-based ceramic slurry was obtained after stirring in the dark for 10 min.

The photosensitive slurry was photo-cured and formed on the DLP printer Photon Mono 4k. The infrared spectra were determined by Fourier transform infrared spectroscopy (FT-IR). The curing thickness of photosensitive resin or slurry at different exposure durations was measured on a coating thickness gauge (HC622) by an iron-based F probe and an iron reference block. The rheological properties of photosensitive slurries were characterized by a rotary rheometer (DESKTOP BKLJ9S3), with steady-state shear rate scanning at room temperature and dynamic temperature, respectively. The thermo-behavior was characterized by differential scanning calorimetry (DSC) on a model Mettler Toledo DSC1 Q2000 thermal analyzer, and thermogravimetric analysis (TGA) on a model Discovery TGA 55 thermal analyzer with an argon gas flow rate of 40 mL/min and a heating rate of 10 ℃/min, respectively. The density of photo-cured printed parts was measured by the Archimede displacement method. The cross-sectional morphology of the material was characterized by field emission scanning electron microscopy (FESEM, Hitachi S4800), and the sample (ion sputter coated Pd layer) was fixed on the sample stage with conductive adhesive at an acceleration voltage of 5 kV and a vacuum degree of ≤ 10^-4 Pa.

PSZ-ViH with vinyl as side groups can be chemically modified with 2-Isocyanatoethylacrylate, and PSZ-ViH-ICA shows the maximum light-curing depth compared with PSZ-TViH-ICA and PSZ-H-ICA. Liquid photoinitiator TPO-L can equilibrate light reactivity and shelf-life via optimizing the TPO-L amount, leading to a good balance of transition depth (D_p=63.09 μm) and threshold exposure intensity (E_c=3.94 mJ/cm²). As a result, TPO-L can be chosen as a suitable photoinitiator in DLP processing for polysilazane slurry. Among the ceramic powders introduced in the slurry, the light-curing depth follows an order of SiO₂>Al₂O₃ > ZrO₂ > Si₃N₄ > AlN. SiC slurry shows a low light-curing depth, while ZrB₂ slurry cannot be light cured totally. Silicon nitride powder is applied as a slurry additive due to the proper light-curing depth and similar chemical components compared with polysilazane adhesive. Ideal light reactivity and higher material density can be realized by synergistic effect of combination addition of micro-sized and nano-sized Si₃N₄. Based on the model of the relationship between transition depth (D_p) and threshold exposure intensity (E_c), the processing parameters are determined (i.e., the layer width is 2/3 of transition depth, the exposure time is adjusted according to three times of threshold exposure intensity). DLP pringting with a high precision of polysilazane slurry can be realized for the production of complex structures (e.g., cellular structure). An interlayered adhesion occurs and the width of single layer is almostly equal to the setting value via analyzing the fracture morphology of light-curing samples with different powder contents and particle sizes.

The distribution of vinyl groups in polysilazane molecules significantly affected the crosslinking density and curing depth. Polysilazane PSZ-ViH containing vinyl side groups had a larger photopolymerization thickness than PSZ-TViH with terminated vinyl groups due to the uniform distribution of active sites in the former.

The photosensitizer screening experiment showed that liquid 2,4,6-trimethylbenzoyl phosphate ethyl ester TPO-L balanced the photo-curing activity and storage stability. The balance between transmission depth and critical exposure intensity could be achieved via optimizing the TPO-L dosage, making it a suitable photosensitizer for polysilazane slurry.

Oxide/nitride powders (such as SiO₂ and Si₃N₄) could ensure a light penetration due to their low refractive index and light color, while carbide/boride powders (such as SiC and ZrB₂) could suffer from severe light attenuation due to their high refractive index and dark color. The density of the photocured sample increased to 1.19 g/cm³ via mixing nano-/micro-sized ceramic powders (i.e., 5% 2 μm Si₃N₄ and 5% 20 nm Si₃N₄), and reducing the light scattering loss (i.e., transmission depth 52.80 μm), which verified the feasibility of micro-/nano-sized synergy in photosensitive polysilazane slurry.

Based on the theoretical model of transmission depth D_p and critical exposure intensity E_c, the processing parameters in DLP were proposed, i.e., the layer thickness was set at 2/3 of the transmission depth (h=2D_p/3), and the exposure time was calibrated to equal to three times of the energy of the critical exposure intensity (t=3E_c/I), thus achieving a high-precision DLP printing of complex structures such as honeycomb.

This study systematically analyzed the chemical composition, phase, firing temperature and atmosphere of Han Dynasty lead glazed pottery unearthed from the Yangguanzhai Site, China, through X-ray fluorescence spectrometer (XRF), X-ray diffractometer (XRD), Raman spectrometer (Raman), thermal expansion meter, X-ray photoelectron spectrometer (XPS), etc., and explored its raw material composition and firing process. The results show that the chemical composition and phase of all sample bodies are similar to those of the clay in the burial area of the Yangguanzhai site, so the raw materials used for making the bodies are all local clay. The glaze colors are divided into three types, i.e., yellow, green and yellow-green. The yellow glaze mainly uses Fe₂O₃ provided by the clay for making the body as a coloring agent, while the green glaze mainly uses CuO provided by bronze as a coloring agent. The content of Fe₂O₃ and CuO in the yellow-green glaze is between the two. Because the melting point of clay is higher than that of bronze, yellow glaze needs to increase lead-rich raw materials and reduce silicon-rich raw materials to lower the melting temperature of the glaze, resulting in yellow glaze showing the characteristic of "high lead and low silicon", while green glaze is the opposite, with yellow-green glaze lying between the two. Although there are differences in the types of colorants and glaze formulas, the samples of the three glaze colors are all fired in an oxidizing atmosphere at the firing temperatures controlled at 850-950 ℃.

In this study, we analyzed the chemical composition and phase composition of the body and glaze in 29 samples to investigate their raw materials and firing techniques by XRF, XRD, Raman spectroscopy, and other techniques.

Based on the colorimetric parameter analysis of glaze samples, they can be categorized into three types, i.e., yellow, green, and yellow-green. The saturation (C*) of yellow and yellow-green glazes exhibits a significant variation, while green glazes show a greater consistency. This variation is correlated to the types and concentrations of colorants in the glazes. The body color is uniform and stable, with coloration primarily influenced by saturation. All the body samples are colored with Fe₂O₃ and TiO₂, exhibiting the similar chemical compositions and phase characteristics. This indicates that the body material likely originates from the same type of common, easily fusible clay, presumably sourced from the Yangguanzhai site. The chemical composition of the glaze layers reveals that yellow glazes have the lowest SiO₂ content and the highest PbO content, while green glazes exhibit the opposite pattern. This may be related to coloration requirements and the fluxing effect of PbO. The coloring agents originate from bronze, and the glaze materials incorporate clay from the body production process as an iron source. The XRD patterns and Raman spectra further confirm the presence of quartz, feldspar, mica, and hematite phases in both body and glaze. The XPS analysis reveals Fe³⁺ as the predominant iron species. Combined with thermal expansion measurements indicating firing temperatures at 850-950 ℃, these results collectively confirm the samples are fired in an oxidizing atmosphere.

The lead-glazed pottery bodies of the Han Dynasty could be brick red in color, with Fe₂O₃ and TiO₂ as colorants. Their chemical composition and phase were highly consistent with the clay of the site, and the components of the bodies with different glaze colors were similar. They had the characteristics of common fusing clay, indicating that the raw materials for making the bodies were taken from the local soil and fired locally. The lead glazed pottery of the Han Dynasty haf three glaze colors, i.e., yellow, green and yellowish-green. The yellow glaze mainly usef Fe₂O₃ as the main colorant, while the green glaze mainly used CuO. The content of Fe₂O₃ and CuO in the yellowish-green glaze was between the two. Since the correlation of Fe₂O₃-TiO₂ in the body and glaze was consistent, and hematite appeared in both glazes, indicating that the clay used for making the body was used as the iron source during glaze production. There could be a positive correlation between CuO and SnO₂ in the glaze, indicating that CuO originated from bronze. Because the melting point of clay was higher than that of bronze, the required PbO content was also higher. Therefore, yellow glaze showed the characteristics of low silicon and high lead, and was prone to "silver glaze" diseases. However, the correlation between SiO₂ and Al₂O₃ in the body and glaze was inconsistent, indicating that silicon-rich raw materials such as quartz sand were added to the glaze. The lead-glazed pottery of the Han Dynasty was all fired in an oxidizing atmosphere, with the firing temperature controlled at 850-950 ℃. The analysis showed that although there were differences in glaze colors, the similar process conditions were adopted for the firing temperature and atmosphere.

This review summarizes recent research on the preparation of Si—O—C ceramic composite absorbing materials by a precursor conversion method from multiple aspects. Particle reinforced Si—O—C ceramics suppress the volume shrinkage of sintered products and improve the yield of ceramics. Porous Si—O—C ceramics cause multiple reflections of electromagnetic waves entering the interior of the material, prolonging the propagation path and helping to improve impedance matching. Introducing heterogeneous element M into Si—O—C ceramics can alter the phase separation and crystallization behavior, and improve the thermal stability of Si—O—C ceramics. Fiber reinforced Si—O—C ceramics achieve a structural and functional integration. However, the manufacturing accuracy of complex structures is limited, and traditional mechanical processing is difficult to achieve high-precision forming of complex lattice structures. Porous Si—O—C ceramic composite absorbing materials face a challenge of balancing structure and performance, and the porosity is difficult to accurately control, with pore size, shape, and distribution being disordered. The interface bonding and phase separation problems of heterogeneous element modified Si—O—C ceramics are prominent, and interface defects are easily formed between heterogeneous phases due to significant differences in chemical properties. Fiber reinforced Si—O—C ceramic composite absorbing materials have both structural load-bearing and absorbing functions, but there is a limited research on the effect of external loads on their absorbing performance at high temperatures.

The comparison of the effect of different sintering aids on the properties of aluminum nitride ceramics indicates that the oxide sintering aid has the most significant effect on the improvement of thermal conductivity and the most mature application technology. However, the sintering temperature required is relatively high, and the second phase of grain boundary generates, affecting the high-temperature performance. It is more suitable for high performance electronic packaging substrate materials. Fluoride sintering aids can significantly reduce the sintering temperature and directly deoxygenate through gas phase volatilization. There is no residual second phase in the grain boundary, but the high temperature volatiles will corrode the sintering equipment, and the sintering process is difficult to control, which is not suitable for industrial production. The composite sintering aid can further reduce the sintering temperature or optimize the grain boundary phase through the synergistic effect, but the formula design is more complicated, and the mechanism of action still needs to be further explored, which is suitable for the pursuit of extreme performance or specific functions. The application cost of other sintering aids is low, but the research is less, the universality is low, and it is still in the experimental research stage.

In the future, advanced characterization techniques can be used to reveal the mechanism of sintering additives, the migration path of oxygen impurities and the dynamic evolution process of grain boundary phase in the sintering process, which can provide a theoretical support for the design of sintering additive system. Nano- or submicron-sized sintering aids are obtained via optimizing the preparation process of sintering aids. Therefore, the utilization efficiency of sintering aids is improved, which is helpful to achieve densification at a lower addition amount. In addition, it can also be devoted to the development of new sintering additives, such as low rare-earth, no rare-earth or no residual sintering additive system, which can effectively reduce the residual impurities at the grain boundary and purify the grain boundary structure. A new type of nitrogen oxide grain boundary phase is constructed via accurately controlling the sintering atmosphere and the proportion of elements in the sintering aid. It can react with Al₂O₃ to form a rare-earth aluminum nitrogen oxide with a higher thermal conductivity and a better electrical insulation or JEM phase and other crystalline phases to replace the low thermal conductivity aluminate glass phase.

This review systematically analyzes the structure-property-processability relationships of CMA materials, highlighting the fundamental contradiction between their excellent performance and challenging densification. A strategic shift toward "performance adaptation and defect transformation" is proposed rather than pursuing densification at all costs, i.e., utilizing plate-like CMA grains as reinforcing phases in monolithic refractories, and exploiting decomposition behavior for lightweight structure design.

Future research directions include, 1) multi-scale mechanistic studies combining first-principles calculations, phase-field simulations, and in-situ characterization; 2) systematic investigation of structure-property relationships in CMA-based monolithic systems; and 3) exploration of novel composites and applications in emerging high-temperature processes. Through such integrated approaches, CMA materials are positioned to contribute significantly to the green transformation of high-temperature industries as environmentally friendly, high-performance refractories.

In summary, the toughening of Al₂O₃-based ceramics evolves from single-mechanism approaches to multi-scale, multi-mechanism synergistic strategies. The fracture toughness of Al₂O₃ composites is increased by 3-4 MPa·m^1/2 for monolithic alumina and by 10 MPa·m^1/2 for ZrO₂-toughened alumina (ZTA) and SiC whisker-reinforced systems. These materials are applied in high-performance cutting tools, ceramic armor, aero-engine hot-section components, semiconductor packaging substrates, and artificial joints. Nevertheless, several critical issues must be addressed to further advance their application:

1) Future research should focus on elucidating the coupled effects of multiple toughening mechanisms through in-situ characterization and multi-scale simulation. Understanding how cracks interact with complex microstructures will enable the design of materials with tailored energy dissipation pathways.

2) Advanced manufacturing techniques, particularly additive manufacturing, offer some opportunities for fabricating complex biomimetic architectures and compositionally graded structures. However, some issues such as fiber damage during sintering, dispersion of nano-reinforcements, and interfacial control must be resolved. External field-assisted techniques (e.g., magnetic or ultrasonic fields) can enable controlled alignment of reinforcements.

3) As application demands become more stringent, future Al₂O₃-based composites must exhibit high toughness and meet requirements for thermal shock resistance, oxidation resistance, electrical conductivity or insulation, and biocompatibility. This calls for a holistic design approach that integrates material selection, microstructure engineering, and performance optimization.

In summary, the development of high-performance Al₂O₃-based ceramic composites is moving toward greater complexity and functionality. With continued innovation in toughening mechanisms, processing technologies, and performance evaluation, these materials are expected to play an increasingly vital role in advanced engineering applications.

After decades of research, combustion synthesis of aluminum nitride powder successfully achieves a technological transition from ultra-high pressure to low/near-atmospheric pressure processing. There is also a relatively systematic understanding of the Al-N₂ combustion reaction process. Nevertheless, this technology is not used in industry. The main concern is an inferior powder performance, compared to the international start-of-the-art. The combustion-synthesized AlN powder has two main issues, i.e., broad particle size distribution and low specific surface area. The fundamental reason is a lack of in-depth understanding on the mechanism underlying the Al-N₂ combustion process. Therefore, a future research should develop a coordinated approach integrating theoretical depth with engineering application. In the theoretical realm, it is essential to conduct a thorough analysis of the reaction mechanism at the Al-N₂ combustion interface. This involves elucidating the morphological evolution of the powder via the in-situ dynamic characterization, clarifying the interaction between combustion wave parameters and powder performance. This provides a scientific basis for overcoming the performance limitations of combustion-synthesized AlN powder. Also, engineering requires a systematic development of post-treatment processes to improve sintering activity and batch stability in combustion-synthesized AlN powder. Concurrently, a reliable "burning product iteration" mechanism must facilitate its transition to industrial application.

Halide SSEs are regarded as ideal candidates for high-energy-density ASSBs owing to their high ionic conductivity, superior electrochemical stability, and good processability. Nevertheless, cathode interfacial instability remains a principal bottleneck in practical applications. Although notable advances have been achieved in materials optimization, interfacial engineering, and structural design, several scientific and engineering challenges remain unresolved.

1) Intrinsic materials stability. Under high-voltage operation, the chemical and electrochemical stability of halide SSEs are still limited. Anion substitution, cation doping, and high-entropy strategies can partially expand these windows, yet their action mechanisms and the governing rules for interfacial electronic-structure modulation are not fully elucidated. Future studies should integrate experiment and theory to establish quantitative links among chemical composition, electronic structure, and stability, considering density of states, space-charge layers, and band alignment at interfaces, to derive design principles for interfacial stabilization.

2) Construction and evolution of interfacial structures. Current efforts focus on electrolyte modification or cathode surface treatments, forming passivating layers from electrolyte decomposition or applying protective coatings to block direct contact between active materials and the electrolyte. Building on this, priority should be given to controllable synthesis that delivers nanoscale, uniform interfacial contact while avoiding byproducts and voids-key to enhancing electrochemical stability. Gradient architectures, core-shell designs, and in situ-formed interphases are promising, but their cycling evolution and mechanical matching require deeper investigation. In parallel, combining single-crystal cathodes with highly stable halide SSEs may offer a new balance between energy density and interfacial stability.

3) Processing and manufacturability. Halide-based ASSBs still face challenges in scalable fabrication and environmental sensitivity. Many halide electrolytes are extremely sensitive to moisture and polar solvents, limiting the direct use of conventional wet processes. Priority should be placed on developing coating, dry pressing, and lamination routes in low-polarity or non-solvent environments, and on mapping how processing parameters (pressure, temperature, atmosphere) affect interfacial structure and performance to unify electrochemical metrics with manufacturability.

In summary, halide SSEs present a compelling suite of advantages for ASSBs, yet cathode interfacial stability remains the key constraint on performance and deployment. Research on halide cathode interfaces is transitioning from mechanistic elucidation to controllable construction and engineering implementation. Future efforts should pursue coordinated advances in materials optimization, structural design, and process development to enable safe, high-energy-density storage. Through the integration of multiple strategies, halide ASSBs hold promise for achieving high energy density, long cycle stability, and industrial viability-advancing ASSBs technology and underpinning safer, more efficient energy-storage systems.