Abstract
Using a simple nearest-neighbour model, published measurements of the thermodynamic activity and the formation enthalpy of CoG are fitted. In combination with vacancy measurements each fit yields a set of four interaction energies, which agree very well. The interaction energy between two gallium nearest neighbours is estimated by use of the Miedema model (1979, 1980) of cohesion in alloys. Knowing all the interaction energies in CoGa the vacancy concentration on the Ga sublattice and the Ga atom concentration of the Co sublattice can be calculated. This leads to very reasonable values. By comparing triple-defect disorder with substitutional disorder it is shown that the interaction-energy parameter set is able to account for the special defect structure of CoGa.