A thermodynamic evaluation of the simplesolution treatment of the Ga-P, In-P and Ga-As systems

Abstract

Compositions and vapor pressure along the group III-rich liquidus of the Ga-P, In-P and Ga-As systems have been used to compare the simple solution interaction parameters obtained both from the liquidus and from the vapor pressures. When the available thermodynamic data are used for the pure P or As liquid reference state, the interaction parameters from the liquid and vapor are different. This disagreement arises from the use of reference state vapor pressures for pure liquid As and P which do not take into account the fact those liquids are highly associated in the temperature range where there are experimental data. When modified reference state pressures are used, the simple solution interaction parameters obtained with critically selected liquidus compositions and with vapor pressures are the same. In all cases the simple solution approximation is consistent with a third law treatment of the vapor pressure data which yields for each system a standard heat for the reaction A III (s)+1/2C 2 v (g)≈A III C v (s). The recommended best standard heats are −44.5±0.5 kcal mole −1 for Ga-As, −45.4±0.5 kcal mole −1 for Ga-P and −35.0±1.0 kcal mole −1 for In-P.