Equilibrium vacancies in Cu and Ag alloys with electropositive solutes

Abstract

Abstract A new method is presented for the calculation of interaction energies of a vacancy-impurity pair and of higher-order complexes from the vacancy formation energy in pure metals and the concentration dependence of the effective formation energy in alloys. In terms of a modified complex model introduced by Berces and Kovacs, changes in the formation entropy of vacancy-impurity complexes compared with that of free vacancies as well as non-random solute distributions around vacancies are taken into account. The treatment is applied to effective vacancy formation energies as a function of alloying in several silver and copper systems with electropositive impurities obtained by resistivity measurements and positron annihilation. Vacancy impurity binding entropies of about k (Boltzmann's constant) are observed. The corresponding binding energies vary from −0·10 to −0·20 eV.