PHASE-DIAGRAM AND DIFFUSION PROPERTIES OF THE QUASI-BINARY SYSTEM (SN,PB)S

The phase diagram of the quasibinary system (SnkPb1-k) S is investigated by electron probe microanalysis, by differential thermal analysis and from X-ray diffraction patterns. At temperatures below T almost-equal-to 850 K the phase diagram is characterized by a broad miscibility pp between the PbS-rich cubic phase and the SnS-rich orthorhombic phase. At higher temperatures there exist two miscibility gaps: a narrow structural pp and a broad ''spinodal'' gap within the orthorhombic phase. For the orthorhombic phase, the interdiffusion coefficient for the Sn/Pb exchange is determined for the temperatures 900 K and 975 K. From the experimental data the interaction parameters and the free enthalpy functions g(k, T) for the cubic and the orthorhombic phase are calculated. By application of the four particle cluster model, the energy dependent cluster probabilities as well as pair formation energies for the metal sublattice are determined. The thermodynamic factor for the Sn/Pb interdiffusion can be explained as a function of these energies.