Medium-entropy ceramic aerogels for robust thermal sealing

Thermal sealing is essential to prevent thermal runaway in aerospace and mechanical fields. Ceramic aerogels are attractive candidates but often show limited thermomechanical performance and thermal radiation opacification that may lead to catastrophic failure. Here, we report medium-entropy design and fabrication of (Ti_0.42Zr_0.42Y_0.08Si_0.08)O_2.08 fibrous aerogels with ultrahigh thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels feature mechanical flexibility with up to 95% compressive strain, 30% non-linear fracture strain and 99% bending strain, and thermostability with a working temperature up to 1400 °C and negligible strength degradation after sharp thermal shocks. The incorporated titania substantially enhances the reflection of thermal radiation and one of the lowest thermal conductivities of 89 mW m⁻¹ K⁻¹ at 1000 °C is achieved among aerogels to date. The medium-entropy-derived ultrahigh thermomechanical properties and ultralow thermal conductivity establish a set of fundamental considerations in material design for robust thermal sealing.