Ordering phenomena in Na-Ga and Na-Sn molten alloys

The quasilattice approximation (QLA) has been applied to study the alloying behaviour of Na-Ga and Na-Sn molten alloys by assuming the formation of complexes of the form Na5Ga8 and Na4Sn3. This has been used to obtain the concentration dependence of the free energy of mixing, the long wavelength limit of the concentration-concentration fluctuations and the ordering parameter alpha(1). Our calculations yield for both alloys, qualitative agreement with experiment about the concentrations at which phase separation or compound formation occurs in the alloy. In the case of Na-Ga, however, because of the relatively large asymmetry in the concentration dependence of its free energy of mixing and possibly the nature of the complex chosen, the calculated results when compared with experiment are not as good as that for Na-Sn. For Na-Ga, we have also calculated the higher order conditional probabilities using the four atom cluster model (FACM) this has made it possible to calculate another value for alpha(1). A comparison of the two values of alpha(1), computed, enables us to obtain better insight to the limit of applicability of each of the models.