Comprehensive thermodynamic description of the quasiternary system PbTe–GeTe–SnTe

The equilibrium phase diagram of the quasiternary system PbTe–GeTe–SnTe was studied experimentally in the ranges of spinodal demixing and (solid + liquid) equilibrium by means of X-ray diffraction (XRD), electron microprobe analysis (EMA) and differential thermal analysis (DTA). A model description of the phase diagram was done on the base of composition dependent interaction parameters, which were determined for the solid and the liquid phases. The interaction parameters for the quasibinary systems were recalculated in order to reach better correlation between all experimental data. It was shown that the quasiternary phase diagram can be principally described using the interaction parameters for the quasibinary subsystems, but an additional ternary interaction parameter has also to be considered. The local structure of the quasiternary solid solution is described by a four-particle cluster model. Due to the tendency of the solid solution to demix, the probability of the (GeGeGe)Te cluster was found to be higher and that of the (PbGeGe)Te cluster to be lower than it is expected for the purely statistical distribution of the clusters.