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.

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.

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.

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.

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.

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.

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.