Thermal Coefficient of Expansion of an Activated Vacancy in Zinc from High-Pressure Self-Diffusion Experiments

Abstract

The coefficient of self-diffusion along the principal axes in zinc was obtained over the temperature range 300-400\ifmmode^\circ\else\textdegree\fi{}C, and over the pressure range 0-9 kbar. The unusually high precision of 2% in the measurement of the vacancy activation volumes was achieved by means of a novel technique that insured temperature reproducibility in the diffusion zone of \ifmmode\pm\else\textpm\fi{} 0.2\ifmmode^\circ\else\textdegree\fi{}C at high pressure. The activation volumes for diffusion, associated with the basal and nonbasal vacancy mechanisms are found to be temperature dependent, isotropic, and approximately proportional to $T$. Hence the thermal coefficient of expansion of an activated vacancy is given by ${\ensuremath{\alpha}}_{v}={T}^{\ensuremath{-}1}$, and is about 15 times larger than the thermal coefficient of expansion of the perfect lattice. The activation entropy is pressure dependent, whereas the activation enthalpy is pressure independent to within the experimental uncertainty.