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Thermal evolution of free volumes and of crystallization in amorphous Si–B–C–N ceramics

Abstract We report on the crystallization behavior of initially amorphous precursor-derived Si3B1C4.3N2 ceramics, making use of macroscopic and atomic scale investigation techniques. As derived from our kinetic studies upon heating, the following temperature sequence of solid state processes is observed with approximately the same kinetic time constants: after an initial densification in the amorphous state (1673K), crystallization occurs (1873K) with subsequent strain relaxation and disappearance of nanovoids (2073K). This behavior indicates an increasing activation enthalpy of the atomic mechanisms giving rise to these processes when the annealing temperature is increased. The nanovoids may be located in the turbostratic BNCx layers as derived from positron annihilation studies. For grain growth at high temperatures an activation energy of HG=3.9eV is derived.