A Quasi-lattice Theory for Compound Forming Molten Alloys

The complex formation model of Bhatia and Hargrove (BH) to explain the thermodynamic properties of compound forming A-B alloys is reformulated using a quasi-lattice picture. The formulation is explicitly carried out to an approximation where the pseudo-ternary alloy (of A and B atoms and AμB_V complexes (μ, v small integers)), envisaged in BH, is treated in the quasichemical approximation. It is advantageous over BH in two major respects: Firstly, it gives useful insight into the two approximations used in BH, since these follow from it by simply going to a lower (zeroth) approximation and setting the coordination number z of the alloy to be z = 2 and z =∞. Secondly, unlike the BH approach, it provides also an expression for the short range order parameter α₁, for nearest neighbours. The effect of varying z in the formulae is examined and a brief discussion of α₁ is given.