Superelastic High‐Entropy Oxide Ceramic Aerogels for Thermal Superinsulation and Sealing at Extreme Conditions

Abstract The lightweight ceramic aerogels are plagued by thermal instability and mechanical degeneration at extreme conditions. In this study, a high‐entropy oxide ceramic of (Gd 1/2 Lu 1/2 ) 2 (Ti 1/3 Zr 1/3 Hf 1/3 ) 2 O 7 (GLTZH) is prepared through a molecular synthesis route of pyrolytic solid‐solution reactions. The atomic resolution observations visualize the phase transition of polyacetylacetonato metal complexes into a defect‐fluorite structured high‐entropy oxide after thermal treatment at 200 to 1100 °C. The GLTZH oxide demonstrates exceptional crystallographic stability without severe grain growth, and element segregation appeared under prolonged exposure to extremely high temperature (≈1500 °C). This originates from the intricate coupling mechanism among entropy‐driven lattice distortion, high‐entropy stabilization, and orbital hybridization effects. Furthermore, GLTZH‐based lightweight nanofiber aerogel is constructed through electrospinning and followed by thermal annealing at 1000 °C. This architectured high‐entropy ceramic aerogel manifests unprecedented thermomechanical properties, including superelastic compressibility of 98% from −196 to 1500 °C, and thermal superinsulation capacity (24.14 mW·m −1 K −1 at room temperature, 81.21 mW·m −1 K −1 at 1000 °C). Due to superior performances beyond most conventional ceramic counterparts, the high‐entropy GLTZH paves a new pathway for advanced ceramic aerogel design in thermal insulation across a wide temperature range, such as thermal protection of hypersonic aircraft.