Thermodynamics and point defects in the B2 intermetallic phase PdIn

The X-ray and bulk densities of PdIn alloys have been determined at ambient temperature on samples annealed at 1273 and 1373 K and quenched in water-ice mixtures. From these measurements the vacancy concentrations in this intermetallic phase have been obtained as a function of In concentration at these two temperatures. In addition, a generalized thermodynamic model is presented which considers the existence of antisite and vacancy defects on both sublattices without any dilute solution approximations. This model uses three energy parameters, whose values have been obtained for PdIn using the measured vacancy concentrations and the chemical potentials of In. This model is able to describe all the available vacancy data and is suitable for calculating these values at compositions and temperatures when such data are not available. In addition, the model permits the calculation of the concentrations of the minority point defects. It is shown that dilute-solution approximations, which have invariably been used in this kind of modelling, are unsatisfactory. The present results and their analysis confirm that PdIn is a near-triple-defect type of intermetallic and not a near-Schottky type, as has been claimed recently.