Reduced standard-state chemical potential method

From a Solution Model. Calculation of the difference in reduced standard-state chemical potentials by methods I or III in the absence of experimental thermodynamic properties for the liquid phase necessitates the imposition of a solution model to represent the activity coefficients of the stoichiometric liquid. Method I is equivalent to the equation of Vieland (106) and has been used almost exclusively in the literature. The principal difference between methods I and III is in the evaluation of the activity coefficients... 

Equilibrium between a pseudobinary III—V solid solution and a ternary liquid solution is described by Equations 3 and 4. By the methods presented in the previous section, the determination of the reduced standard state chemical potential change, 0jq, can proceed in a reliable manner. The other term contained in Equations 3 and 4 is and its determination is discussed here. 

Four different methods were presented to determine the reduced standard state chemical potential change and applied to the Ga-Sb system. It is common practice to use Equation 7 and a solution model representing the stoichiometric liquid activities to determine 0. The solution model parameters are then estimated from a fit of the binary phase diagram. It has been shown that this procedure can lead to large errors in the value of 0. The use of Equation 9, however, gave the correct temperature dependence of 0 and the inclusion of activity measurements in the data base replicated the recommended values of 0Tp. 

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