КВАЗІПОТРІЙНА СИСТЕМА PbS–PbSe–Tl4PbSe3

Анотація

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 physico-chemical 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 PbS_хSe_1-х (х=0–1) phases and one region of their co-crystallization. The widest range of homogeneity has a solid solution PbS_хSe_1-х (х=0–1) based on the initial binary lead chalcogenides. The PbS_хSe_1-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 PbS_хSe_1-х (х=0–1) phases are divided by the line of monovariant eutectic equlibria e2–e1 (800–793K).