Abstract
An improved theory based on the pair approximation is given for the thermodynamic properties of type A 1− x B x C 1− y D y III–V quaternary solid solutions. The theory takes into account the quasi-chemical nature of the nearest neighbor pair distribution, which has been neglected or inadequately treated in previous work. With a suitable thermodynamic treatment, a quasi-chemical equilibrium relation for the nearest neighbor pair distribution is derived. Numerical calculations using available thermodynamic data show that the distribution will deviate appreciably from random mixing values in the In 1− x Ga x P 1− y As y and Al 1− x Ga x As 1− y Sb y systems due to a short-range clustering effect of nearest neighbor pairs with strong bond energy, whereas the deviation will be small in the Al 1− x Ga x P 1− y AS y system. The expressions for the chemical potentials and the activity coefficients of the binary compound components are given. These are readily applicable to phase diagram calculations.
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