Rare-earth-niobate high-entropy ceramic foams with enhanced thermal insulation performance

The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance. In this work, a series of novel rare-earth-niobate high-entropy ceramic foams ((Dy_0.2Ho_0.2Y_0.2Er_0.2Yb_0.2)₃NbO₇) with hierarchical pore structures were prepared by a particle-stabilized foaming method. Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion. The high-entropy ceramic foams exhibit high porosity (90.13%-96.13%) and ultralow thermal conductivity (0.0343–0.0592 W/(m·K)) at room temperature. High-entropy ceramic foam prepared by a 20 wt% slurry sintered at 1500 °C has the porosity of 96.12% and extremely low thermal conductivity of 0.0343 W/(m·K). The existence of walls and secondary pores contributes to reduced thermal conductivity. There is a temperature difference of over 800 °C between frontside and backside of the sample under fire resistance test. The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.