Vacancies and Divacancies in Quenched Gold

Abstract

The behavior of vacancies and divacancies in gold was studied by electrical resistance measurements made after quenching and after annealing. It was found that a small amount of some impurity decreases the effective migration energy associated with the annealing of specimens quenched from 700\ifmmode^\circ\else\textdegree\fi{}C. Therefore most of the experiments used gold having a resistivity ratio $\frac{{\ensuremath{\rho}}_{298\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}}}{{\ensuremath{\rho}}_{4.2\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}}}$ of 4000 or more. The effective migration energy from slope-change measurements was found in these pure samples to depend on both the vacancy concentration and the annealing temperature. These observations suggest that the binding energy of a divacancy is less than 0.15 eV. Other experimental results support this value. Slope-change measurements at 140 and 150\ifmmode^\circ\else\textdegree\fi{}C at low concentration give the migration energy for single vacancies to be 0.94\ifmmode\pm\else\textpm\fi{}0.05 eV. The formation energy of single vacancies was measured by noting the amount quenched in from temperatures below 600\ifmmode^\circ\else\textdegree\fi{}C. This gave ${{E}_{F}}^{v}=0.95\ifmmode\pm\else\textpm\fi{}0.02$ eV. The high-temperature migration energy is therefore 0.85\ifmmode\pm\else\textpm\fi{}0.03 eV. It is shown that the thermal expansion of the lattice accounts for the observed difference between the high-temperature and the low-temperature vacancy migration energy. The divacancy migration energy at 150\ifmmode^\circ\else\textdegree\fi{}C is 0.70\ifmmode\pm\else\textpm\fi{}0.10 eV. The mechanisms responsible for vacancy loss during a quench are discussed. It is shown that dislocations cannot accept vacancies until the supersaturation grows large enough to overcome the line tension. Observations on vacancy loss during quenching are not sensitive to dislocation density. It is suggested therefore that the major loss may occur by the production of vacancy tetrahedra at impurities.