Self-diffusion of¹⁴C in polycrystalline β-SiC

Abstract

The¹⁴C self-diffusion coefficients for both lattice (D ^*_lc ) and grain boundary (D ^*_bc ) transport in high purity CVDβ-SiC are reported for the range 2128 to 2374 K. The Suzuoka analysis technique revealed thatD ^*_bc is 10⁵ to 10⁶ faster thanD ^*_bc ; the respective equations are given by

$$\begin{gathered} D_{I c}^* = (2.62 \pm 1.83) \times 10^8 exp\left\{ { - \frac{{(8.72 \pm 0.14)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ D_{b c}^* = (4.44 \pm 2.03) \times 10^7 exp\left\{ { - \frac{{(5.84 \pm 0.09)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ \end{gathered} $$

A vacancy mechanism is assumed to be operative for lattice transport. From the standpoint of crystallography and energetics, reasons are given in support of a path of transport which involves an initial jump to a vacant tetrahedral site succeeded by a jump to a normally occupied C vacancy.