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

Abstract

Volume self-diffusion in high-purity (1 ppm absolute total impurities) single-crystal tellurium has been determined between 300 and 400\ifmmode^\circ\else\textdegree\fi{}C using $\mathrm{T}{\mathrm{e}}^{127m}$ as the tracer. Along [0001], the data can be represented by $D=1.30\ifmmode\times\else\texttimes\fi{}{10}^{2}\mathrm{exp}[\frac{(\ensuremath{-}1.75\ifmmode\pm\else\textpm\fi{}0.05 \mathrm{eV})}{\mathrm{kT}}]$ ${\mathrm{cm}}^{2}$/sec, whereas $D=3.91\ifmmode\times\else\texttimes\fi{}{10}^{4}\mathrm{exp}[\frac{(\ensuremath{-}2.03\ifmmode\pm\else\textpm\fi{}0.10 \mathrm{eV})}{\mathrm{kT}}]$ ${\mathrm{cm}}^{2}$/sec represents the data along all the atomically equivalent directions perpendicular to [0001]. Above (300\ifmmode\pm\else\textpm\fi{}7)\ifmmode^\circ\else\textdegree\fi{}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.