Квазіпотрійна система PbS–PbSe–Tl4PbSe3

Abstract

Binary and complex chalcogenides of p-elements are perspective objects as a functional materials in the optics and thermoelectric technologies. To the investigation of the phisico-chemical interaction between them its devoted a considerable amount of work. That's why the study of new systems based on the known binary and ternary chalcogenides are actual. The initial compounds of the quasiternary PbS–PbSе–Tl4PbSe3 system had close lattice parameters (for PbS and PbSe compounds), similar structural motives ([PbS6(Se6)] octahedrons). Combination of structural similarity with high functional parameters determine the practicality of the investigation of the phase equilibria in the PbS–PbSе–Tl4PbSe3 system. The aim of the work is the study of the physico-chemical interaction system PbS–PbSе– Tl4PbSe3 determination of the coordinates of invariant points and monovariant lines courses, the homogeneity regions of the initial binary and ternary phases. Using the differential thermal (DTA) and X-ray diffraction (XRD) analyzes the pre-synthesized compounds Tl2Se, PbS, PbSе, Tl4PbSe3 were identified. Established that the obtained compounds are individual phases. Based on the results of the DTA, XRD and microstructural analysis (MSA) the physicochemical interaction in the quasiternary system PbS–PbSе–Tl4PbSe3 were investigated. Established that in quasiternary system PbS–PbSе–Tl4PbSe3 at 573K exist two regions of solid solution based on Tl4PbSe3 and PbSхSe1-х (х=0–1) phases and one region of their co-crystallization. The widest range of homogeneity has a solid solution PbSхSe1-х (х=0–1) based on the initial binary lead chalcogenides. The PbSхSe1-х (х=0–1) solid solution occupies all section PbS–PbSe and extends to 10 mol. % into the system PbS–PbSе–Tl4PbSe3. The solid solution based on Tl4PbSe3 occupies the egde of the PbS– PbSе–Tl4PbSe3 concentration triangle. The width of the solid solution based on Tl4PbSe3 does not exceed 2 mol.% along the PbS–Tl4PbSe3 section and 7 mol.% in the PbSе–Tl4PbSe3. Based on the temperatures of the primary crystallization of alloys the projection of liquidus surface has been studied and built. Established that the fields of primary crystallization of Tl4PbSe3 and PbSхSe1-х (х=0–1) phases are divided by the line of monovariant eutectic equlibria e2–e1 (800– 793K). Key words: Chalcogenides; Thermal analysis; X-ray diffraction; Solid solutions; Isothermal section; Projection of liquidus surface.