Determinations were made of Si self-diffusion in the polymer-derived amorphous ceramic, Si28C36N36, which consisted of amorphous Si3N4 and C phases. This diffusivity governed the transformation of the ceramic from an intermediate amorphous state to a final crystalline state. The Si self-diffusivity was simulated by the diffusion of 71Ge. This was done by using a radiotracer technique in which radioactive 71Ge atoms were implanted. After diffusion annealing, the specimens were serially sectioned by means of Ar+-beam sputtering. The 71Ge diffusivity obeyed the Arrhenius law at 850 to 1300C; with a pre-exponential factor of 0.2m2/s, and a diffusion enthalpy that increased from 4.6eV in as-produced specimens to 5.5eV in 1350C pre-annealed specimens. These results were explained in terms of 71Ge diffusion, in the amorphous Si3N4 phase, which was mediated by smeared-out thermal vacancies.

Diffusion of 71Ge in the Amorphous Ceramic Si28C36N36. S.Matics, W.F.J.Frank: Journal of Non-Crystalline Solids, 2000, 266-269, 830-4