Synergistic promotion of dielectric and thermomechanical properties of porous Si ₃N ₄ ceramics by a dual-solvent template method

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.