Self-Diffusion in Tellurium. I. Anisotropy and Impurity Effect

Volume self-diffusion in high-purity (<1 ppm absolute total impurities) single-crystal tellurium has been determined between 300 and 400°C using $\mathrm{T}{\mathrm{e}}^{127m}$ as the tracer. Along [0001], the data can be represented by $D=1.30\mathrm{}\times {10}^2\exp \left[\frac{(-1.75\mathrm{}\pm 0.05 \mathrm{eV})}{\mathrm{kT}}\right]$ ${\mathrm{cm}}^2$/sec, whereas $D=3.91\mathrm{}\times {10}^4\exp \left[\frac{(-2.03\mathrm{}\pm 0.10 \mathrm{eV})}{\mathrm{kT}}\right]$ ${\mathrm{cm}}^2$/sec represents the data along all the atomically equivalent directions perpendicular to [0001]. Above (300±7)°C, the self-diffusivity is higher perpendicular to the $c$ axis than along [0001]. At lower temperatures, aluminum has been shown to increase, and iodine to decrease, the self-diffusion coefficient of tellurium along both the principal crystallographic directions. The vacancy-formation energy is estimated to be about 1 eV.