Crystallization kinetics of Si₃N₄in Si–B–C–N polymer-derived ceramics

To study the crystallization kinetics of β-Si₃N₄in Si–B–C–N polymer-derived ceramics, the amorphous ceramics with composition SiC_1.6N_1.0B_0.4were synthesized and then isothermally annealed at 1700, 1775 and 1850 °C. The integrated intensities of β-Si₃N₄x-ray diffraction (XRD) patterns were used to examine the course of crystallization. The average size of the Si₃N₄nanocrystallites was analyzed by means of the XRD measurements and energy-filtering transmission electron microscopy. It was realized that the nanocrystallite dimensions change insignificantly within the time period of crystallization; however, they depend significantly on the temperature. Subsequently, the kinetics of the β-Si₃N₄crystallization was analyzed. Consequently, large activation energy in the range of 11.5 eV was estimated. Moreover, continuous nucleation and diffusion-controlled growth have been concluded as the main mechanisms of the crystallization process. Further analysis points at the crucial role of the nucleation rate in the crystallization kinetics of β-Si₃N₄.