In situ formed multiphase ceramics with composition-dependent thermal expansion and synergistically enhanced thermal-mechanical properties for thermal protection applications

Advanced thermal protection materials faced a trade-off among low thermal conductivity, high toughness, and high-temperature phase stability. In this study, a novel ceramic system, x Gd₂O₃-(1- x )Yb₂O₃-2 x ZrO₂-(2–2 x )SiO₂ (0 ≤ x ≤ 1), was synthesized through an in situ solid-state reaction, achieving composition-dependent variation of the coefficient of thermal expansion (CTE). At 1000 ℃, all of them exhibit relatively low thermal conductivity. The material retains excellent phase stability even after 50 h of heat treatment at 1500 °C. The multiphase synergy between the Gd_9.33(SiO₄)₆O₂ apatite phase and the Yb₂Zr₂O₇ phase with a fluorite structure significantly enhances phonon scattering, reducing the thermal conductivity of the x = 0.7 composition to 1.24 W·m⁻¹·K⁻¹. Meanwhile, the fracture toughness was improved to 2.77 MPa·m^1/2 through a multi-scale toughening mechanism. This work provides a novel strategy for achieving synergistic optimization of the thermal and mechanical properties of thermal protection materials.