Diffusion of 71Ge in the amorphous ceramic Si28C36N36

The objective of this research was the determination of the Si self-diffusivity in the polymer-derived amorphous ceramic Si28C36N36, which consists of two amorphous phases, a-Si3N4 and a-C. This diffusivity is of technological importance, since it contributes to the ceramic’s transition from its intermediate amorphous to its final crystalline state. The Si self-diffusion was simulated by the diffusion of 71Ge. This was done by a radiotracer technique, in which radioactive 71Ge atoms were implanted. After diffusion annealing, the specimens were serially sectioned by Ar+-beam sputtering. The 71Ge diffusion coefficients obey Arrhenius laws in the temperature regime investigated (850–1300°C) with a pre-exponential factor of 0.2 m2 s−1 and a diffusion enthalpy that increases from 4.6 eV in as-produced to 5.5 eV in 1350°C-pre-annealed specimens. These data are interpreted in terms of 71Ge diffusion in the a-Si3N4 phase which is mediated by smeared-out thermal vacancies.