Sustained release of nanocrystal by strong lattice confinement enables flexible ceramic nanofibers for enduring exposure to 1500 °C.

Polycrystalline ceramic fibers are indispensable components in advanced materials systems owing to their unique combination of flexibility, mechanical strength, high melting point, and elastic modulus. However, the prolonged energy input at high temperatures dramatically accelerates defect accumulation, eventually leading to rapid degradation of structure integrity and mechanical performance at extreme conditions. Here, we report a strong lattice confinement strategy with sustained release of ceramic nanocrystals (SRC) in fibers, enabling exceptional flexibility and mechanical robustness after continuous exposure at 1500 °C for 15 h. This behavior originates from the strongly suppressed nucleation of the strengthening tetragonal zirconia phase within mullite fiber matrix, which promotes the homogeneous dispersion of nanocrystals throughout the fiber. Acting as a dynamic ceramic reservoir, these nanocrystals are continuously released under thermal input, maintaining fiber intact during service. Beyond demonstrating superior high-temperature durability, this work also stimulates the advancement of ceramic fiber strengthening with dynamic structure evolution from strong lattice confinement.