Scalable Fabrication of Flexible High-Entropy RE ₃ Al ₅ O ₁₂ Garnet Ceramic Fibers for Thermal Insulation in Extreme Environments

As an emerging class of ceramic materials, high-entropy ceramics (HEC) have captured significant interest. Yet, their inherent brittleness and inelasticity restrict broader engineering applications like thermal protection. Here, we report a carboxylic ligand confinement strategy, integrating sol–gel electrospinning with optimized postcalcination treatment, enabling the scalable fabrication of flexible high-entropy (Y 0.2 Yb 0.2 Ho 0.2 Lu 0.2 Er 0.2 ) 3 Al 5 O 12 (RE 3 Al 5 O 12 ) single-crystal fiber films. We initiated the process by preparing an aluminum sol and subsequently coordinating it with carboxylate under hydrochloric acid catalysis. The inorganic colloid growth is modulated by the stoichiometric addition of tartaric acid, forming a hybrid inorganic/organic sol. Then, the sol was electrospun into precursor fiber films followed by calcination at 900 °C to form flexible RE 3 Al 5 O 12 films with a low density of 0.1398 g/cm 3 and a low thermal conductivity of 25.1 mW·m –1 ·K –1 . The HEC film maintains phase stability and structural integrity up to 1600 °C or in liquid nitrogen. In addition, aerogels fabricated by stacking these HEC films demonstrate an 80% strain elastic recovery and exhibit great resistance to thermal shock. This work establishes a strategy for synthesizing lightweight HEC garnet fibers poised for extreme-environment thermal protection systems.