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.

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.

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.

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.

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.