Fig. 3. Compressive test results of nanofiber sponge at high temperatures.

(A) Compression and recovery processes of macroscopic TiO₂ sponge in the flame of an alcohol lamp. (B) SEM image of TiO₂ sponge pressed by a nanoindenter on the loading stage with a MEMS heating system. (C) In situ SEM images of compressive process of TiO₂ sponge at 400°C. The insets show the bending and springback of single nanofiber remarked in (C). (D) Stress-strain curves of TiO₂ sponge with a density of ~40 mg/cm³ at 400°C for 10 cycles. (E) Variation of energy loss coefficient and maximum stress with cycle number of TiO₂ sponge in (D). (F) YSZ sponge heated by a methane flame. (G) Stress-strain curves of YSZ sponge at 800°C for 10 cycles.