Quantitative correlations of deviations from ideality in binary and pseudobinary solid solutions

Deviations from ideal mixing in a number of isostructural binary solid solutions are parameterized using regular and subregular thermodynamic mixing models. Linear correlations between calculated interaction parameters and a term representing the volume mismatch of the two end-members are obtained. These correlations apply to a wide variety of structure types and are found to segregate the solid solutions according to the valence of the ions being mixed. Alkali halide systems show smaller relative deviations than oxide and chalcogenide systems. The ratio of the slopes of these correlations agree with predictions made from consideration of the effective charges of the ions being mixed. The correlations are used to predict the variation of critical temperature, and composition, as a function of component volume mismatch. Calculations of the free energies of transformation of rock salt to nickel arsenide structures and of wurtzite/sphalerite (fourfold coordination) to rock salt/nickel arsenide (six-fold coordination) structures are made using the interaction parameters predicted by the correlations and observed terminal solid solubility data.