Vacancy-Formation Energy and Entropy in Magnesium Single Crystals

Abstract

Macroscopic thermal dilatation coefficients as well as those of the lattice have been precisely measured along principal crystallographic directions of magnesium single crystals in the temperature range between room temperature and 650\ifmmode^\circ\else\textdegree\fi{}C. The vacancy concentration was thus obtained as a function of temperature and it reached the value of 72\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ in the neighborhood of the melting point. An appreciable anisotropy in the atom rearrangement appears during the defect-formation process, which seems to correspond to a preferential climb of edge dislocations in the prismatic planes. From the behavior of the excess in macroscopic dilatation as a function of temperature, the formation energy is found to be 0.58 eV per vacancy, while the formation entropy is practically zero.