Xenon diffusion behaviour in pyrolytic SiC

Abstract

The fractional release of ¹³³Xe, produced in pyrolytic SiC by fission recoil, has been measured below 1753‡ C both in isochronal and isothermal annealings. The release behaviour is interpreted for three temperature ranges; below 1200‡ C, from 1200 to 1400‡ C and above 1400‡ C. The release in the highest temperature region (>1400‡ C) would be due to vacancy mechanism, and the apparent diffusion coefficient is expressed as

$$D = 3.7 \times 10^6 {\text{ exp ( - 157}} \times {\text{10}}^{\text{3}} {\text{/}}RT{\text{) cm}}^{\text{2}} {\text{ sec}}^{{\text{ - 1}}} .$$

The release in the medium temperature region (1200 to 1400‡ C) is probably due to the grain-boundary diffusion coupled with the migration of C or Si atoms in the boundary, and the apparent diffusion coefficient is expressed as

$$D = 8.6 \times 10^{ - 6} {\text{ exp ( - 78}} \times {\text{10}}^{\text{3}} {\text{/}}RT{\text{) cm}}^{\text{2}} {\text{ sec}}^{{\text{ - 1}}} .$$

The release in the lowest temperature region (<1200‡ C) is explained by assuming the interstitial diffusion of Xe ejected from the trapping sites.