Energy‐Filtered TEM Study of Ostwald Ripening of Si Nanocrystals in a SiOC Glass

Sol–gel‐derived SiOC ceramics are metastable glasses that undergo microstructural modifications upon annealing at temperatures exceeding 1000°C. Typically, silicon‐rich SiOC compounds show the presence of a low volume fraction of silicon and silicon carbide nanocrystals upon exposure to 1200°C. Here, the microstructural changes occurring in a Si‐rich SiOC composition after long‐term annealing experiments performed at 1300°C for 1, 10, and 100 h were investigated by high‐resolution (HRTEM) and energy‐filtered transmission electron microscopy (EFTEM), in order to characterize the size evolution of the Si precipitates. The elemental maps obtained through EFTEM analysis indicate that the nanocrystals grow as a function of the annealing time according to the classical mechanism of Ostwald ripening. The estimated diffusion constant of silicon in the SiOC matrix is on the order of 7 × 10 −17 cm 2 /s.