Vacancies in CoGa

Abstract

Thermal and constitutional vacancies are studied for five compositions of the intermetallic compound CoGa. Macroscopic density measurements are used to determine the structural and frozen-in thermal vacancy content. The formation of thermal vacancies is derived from thermal expansion measurements of the macroscopic length and the lattice parameter up to 900°C. The results of these vacancy concentration measurements are interpreted in terms of triple-defect formation. The temperature dependence of the creation of triple defects cannot be described by a simple Arrhenius behaviour. However a simple nearest-neighbour interaction model, with a Bragg-Williams approximation gives a very good description of all results both as a function of temperature and composition. From a simultaneous least-squares fit of all results with this model two energy parameters and a composition dependent triple-defect formation entropy are derived. In this way some insight into the interaction energies in CoGa is obtained.