Phase equilibrium in system Sm2Te3–GeTe

Abstract

Objective. GeTe and some alloys on its basis are prospective materials. There are information on the infl uence of rare earth chalcogenides on thermoelectrically properties of germanium telluride in literature.Synthesis of new complicated triple alloys from the fi elds of solid solutions on the base of initial semiconductive compounds allows me to recommend the obtained materials for usage in different possible fi elds of science and technics.

Purpose. The aim of this work is an investigation of phase equibilibrium interaction in Sm₂Te₃–GeTe system with phase diaqram construction, defi nition of homogenosity fi elds and newsemiconductive phases.

Methods and methodology. The section of Sm2Te3–GeTe was studied by methods of physicalchemical analysis: differential-thermal (DTA), high temperature differential-thermal (HTDT), X-ray phase, microstructural analysis (MSA), as well as measurement of density and micro hardness. DTA was performed with pyrometer HTP-75. HTDT was performed with HTDT-8m (Tmelt ≥ 1500×2000 K) by analogical method. X-ray phase analysis was performed by powder method with X-ray diffractometer DRON-2 (CuKa-radiation with Ni-fi lter). MSA was performed with microscope MIM-8. Micro hardness of alloys was measured with micro- hardness tester PMP-3. Density of alloys was determined by pycnometer test.

Results. Based on data of physical-chemical analysis the diagram of state of Sm₂Te₃–GeTe system has been constructed. The cutting is a guasibinary section of a triple system Ge-Te-Sm. At the ratio of initial tellurides 1:1 (50 mol %) and the temperature 1100 K according to peritectic

reaction m+Sm₂Te₃→GeSm₂Te₄ the triple complex GeSm₂Te₄ is formed. The liquidus of Sm₂Te₃–GeTe system consists of three branches, which are responsible for fusion (melting) of Sm2Te3, GeSm2Te4 and a-solid solutions based on GeTe. X-ray phase analysis of crystallized samples showed, that collection of X-ray refl ections corresponds to the phases Sm₂Te₃ – GeTe , GeSm₂Te₄ and у- solid solutions based on GeTe. In order to determine the dissolution of Sm₂Te₃ in GeTe there has been carried out additional burning of alloys 1,3,5 mol % Sm2Te3 at 920K (time of annealing – 340 hours). After annealing , according to the data of chemical analysis, the dissolution of Sm₂Te₃ in GeTe was 2 mol %. From practical point of view the obtained compound can be a perspective thermoelectrical material for making a positive branch of thermoelement.

Conclusions. Thus, the phase diagram Sm₂Te₃ – GeTe has been constructed. It has been established, that the cutting Sm₂Te₃ – GeTe is a quasibinary section of a triple system Ge –Te– Sm. In the system, at the ratio of initial tellurides 1:1 (50 mol %) an incongruently melting triple compound of in GeSm₂Te₄ composition is formed. On the base of GeTe a narrow fi eld of solid solution is formed.

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