Phase Equilibria in the Ag2Te-PbTe-Bi2Te3 System

Phase equilibria in the Ag2Te-PbTe-Bi2Te3 quasi-ternary system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and emf of concentration circuits with an Ag4RbI5 solid electrolyte. Some polythermal sections and isothermal ( 600 and 800 K) sections of the phase diagram, and also a projection of the liquidus surface were constructed. The primary crystallization fields of phases were determined, and the types and coordinates of invariant and monovariant equilibria were found. The system is characterized by the formation of a wide continuous band of high-temperature solid solutions (gamma phase) with a cubic structure along the PbTe-AgBiTe2 section. With decreasing temperature (T <= 715 K), AgBiTe2 and. solid solutions, close in composition to this compound, experience solid-phase decomposition to form Bi2Te3, ternary tetradymite-like phases of the PbTe-Bi2Te3 boundary system, and the low-temperature phase of Ag2Te.