Si₃N₄ ceramics are promising wave-transparent materials with excellent mechanical and dielectric properties. Vat photopolymerization (VPP) 3D printing provides a strategy for preparing ceramics with controllable complex structures. However, the difficulty in solidifying the slurry due to partial ultraviolet (UV) light absorption and high refractive index by the Si₃N₄ particles during the VPP process severely hampers the molding of Si₃N₄ ceramics. Higher laser power has to be used to increase the curing depth, which generates large internal stresses and leads to the warping of the samples. This paper presents a method to solve the warpage problem during VPP-3D printing using tributyl citrate as a plasticizer. The plasticizer can weaken the force between polymer molecular chains and reduce the internal stress of the green body. The warpage decreases gradually with the increase of tributyl citrate content, and the warpage decreases to 0 when the plasticizer content reaches 30 wt.% at high laser powers from 600 mW to 750 mW. Samples with different layer thicknesses were printed and the optimum thickness of 40 μm was obtained, at which the sintered Si₃N₄ samples possess a unique combination of mechanical properties, including a bending strength of 338.29±12.08 MPa, a fracture toughness of 6.94±0.11 MPa·m^1/2 for the loading direction perpendicular and 5.37±0.99 MPa·m^1/2 for the loading direction parallel to the build surface, respectively. The dielectric constant of all the samples is maintained in the range of 5.462 to 6.414. This work is expected to guide vat photopolymerization and the preparation of complex Si₃N₄ ceramic components.

Porous Si₃N₄ ceramics are promising high-temperature wave transparent materials for use as radomes or antenna windows in hypersonic aircraft. However, a trade-off between the dielectric and thermomechanical properties is still challenging. Therefore, tailoring the microstructure and properties of porous Si₃N₄ is highly important. In this work, porous Si₃N₄ ceramics with uniform and fine structures were obtained via dual-solvent templating combined with the freeze-casting method. The as-prepared porous Si₃N₄ ceramic, with 56% porosity, possesses high mechanical properties, with flexural strength and compressive strength values of 95±14.8 and 132±4.5 MPa, respectively. The uniform spherical pore structure improved the mechanical properties, and the rod-shaped Si₃N₄ grains facilitated crack deflection. The decreased pore size effectively blocks phonon transport, leading to a low thermal conductivity of only 4.2 W/(K·m). Moreover, the porous Si₃N₄ ceramic maintains a small dielectric constant of 3.3, and the dielectric loss is stable between 1.0×10⁻³–4.0×10⁻³, which guarantees its potential application in high-temperature wave-transparent components. These results significantly advanced the development of high-performance wave-transparent materials used in hypersonic aircraft.

ZrP₂O₇ is a promising wave-transparent material due to its low dielectric constant and low dielectric loss, but its inherent phase transition characteristic at approximately 300 °C limits its high-temperature application. Therefore, suppressing the phase transition is necessary for ZrP₂O₇ to serve in extremely harsh environments. In this work, introducing Ti and Hf into ZrP₂O₇ causes significant lattice distortion and an increase in entropy, both of which synergistically limit the crystal structure transformation. In addition, enhanced phonon scattering by mismatch of atomic mass and local distortion leads to a reduction in the thermal conductivity. Lattice distortions also cause changes in both bond length and tilting angle, so that (Ti_1/3Zr_1/3Hf_1/3)P₂O₇ does not undergo sudden expansion as does ZrP₂O₇. (Ti_1/3Zr_1/3Hf_1/3)P₂O₇ maintains excellent dielectric properties, which highlights it as a promising high-temperature wave-transparent material.

In this study, (Cr_1/3/Ta_2/3) non-equivalent co-doped Bi₄Ti₃O₁₂ (BIT) ceramics were prepared to solve the problem that high piezoelectric performance, high Curie temperature, and high-temperature resistivity could not be achieved simultaneously in BIT-based ceramics. A series of Bi₄Ti_3−x(Cr_1/3Ta_2/3)_xO₁₂ (x = 0–0.04) ceramics were synthesized by the solid-state reaction method. The phase structure, microstructure, piezoelectric performance, and conductive mechanism of the samples were systematically investigated. The B-site non-equivalent co-doping strategy combining high-valence Ta⁵⁺ and low-valence Cr³⁺ significantly enhances electrical properties due to a decrease in oxygen vacancy concentration. Bi₄Ti_2.97(Cr_1/3Ta_2/3)_0.03O₁₂ ceramics exhibit a high piezoelectric coefficient (d₃₃ = 26 pC·N⁻¹) and a high Curie temperature (T_C = 687 ℃). Moreover, the significantly increased resistivity (ρ = 2.8×10⁶ Ω·cm at 500 ℃) and good piezoelectric stability up to 600 ℃ are also obtained for this composition. All the results demonstrate that Cr/Ta co-doped BIT-based ceramics have great potential to be applied in high-temperature piezoelectric applications.

Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, calcium–magnesium–alumina–silicate (CMAS) corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature. Therefore, it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures. Herein, the interaction between RE₂SiO₅ and CMAS up to 1500 ℃ was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca₂RE₈(SiO₄)₆O₂) fast along the [001] direction, and the precipitation of short and horizontally distributed Ca₂RE₈(SiO₄)₆O₂ grains was accelerated during the cooling process. The increased temperature increases the solubility of RE elements, decreases the viscosity of CMAS, and thus elevates the corrosion reaction rate, making RE₂SiO₅ fast interaction with CMAS and less affected by RE element species.

(Bi_0.5Na_0.5)TiO₃ (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, <00l> textured Nb⁵⁺-doped 0.8(Bi_0.5Na_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi₄Ti₃O₁₂ as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient ( $d_{33}^{*}$) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 10⁵ cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

Low thermal conductivity, compatible thermal expansion coefficient, and good calcium- magnesium-aluminosilicate (CMAS) corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics. Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance. However, the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application. Inspired by the high entropy effect, a novel rare earth monosilicate solid solution (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ was designed to improve the overall performance. The as-synthesized (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ shows very low thermal conductivity (1.07 W·m^-1·K^-1 at 600 ℃). Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties. The thermal expansion coefficient of (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ can be decreased to (4.0-5.9)×10^-6 K^-1 due to severe lattice distortion and chemical bonding variation, which matches well with that of SiC ((4.5-5.5)×10^-6 K^-1). In addition, (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ presents good resistance to CMAS corrosion. The improved performance of (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ highlights it as a promising environmental barrier coating candidate.