TRIANGULATION OFTHE Cu-Sb-Se SYSTEM

Abstract

Thermoelectric technologies allow the direct conversion of waste heat into electricity. A new strategy for finding promising thermoelectric materials is to study the phase diagrams of multicomponent systems. Analysis of recent investigations indicates high perceptivity of Cu2Se phase, due to abnormally low values of the thermal conductivity and high values of electrical conductivity. Other thermoelectric materials based on copper have attractive properties, such as: diamond-like compounds, argyrodites, oxiselenides, tetrahedron-type compounds and others. Due to this a more detailed investiation of the Cu–Sb–Se system are actually. An important step in the study of the system is the determination of quasi-binary sections by carrying out the triangulation. For this purpose, the quasi-binarity of sections in the ternary Cu–Sb–Se system at a temperature of 523 K was determined by X-ray diffraction analysis. Since the annealing temperature in the synthesis process is 523 K, six binary Cu2Se, CuSe, CuSe2, Cu1.6Sb0.4, Cu2Sb, Sb2Se3 and three ternary compounds CuSbSe2, Cu3SbSe3, Cu3SbSe4 took part in the triangulation of the system. Analysis of the early studies showed the presence of three quasi-binary sections in the Cu–Sb–Se system: Cu2Se – Cu3SbSe3, Cu3SbSe3 – CuSbSe2 and CuSbSe2 – Sb2Se3, and the character of the remaining 12 sections requires experimental studies. The quasi-binary section of Cu2Se-Sb2Se3 divides the general system of Cu-Sb-Se into two subsystems: Cu2Se-Sb2Se3-Se (30 intersection points) and Cu-Sb-Sb2Se3-Cu2Se (13 intersection points). To optimize the process of triangulation, it was decided to carry out it in stages: synthesis and study of the point in the most informative phase field with following separation and exclusion of quasi-binary and non-quasi-binary sections. Such approach makes it possible to reduce the number of syntheses and the number of used substances. Phase analysis was performed by comparing experimental and calculated from the literature powder patterns of phases present in the systems Cu2Se-Sb2Se3-Se and Cu-Sb-Sb2Se3-Cu2Se. The obtained results indicate that in the subsystem Cu2Se-Sb2Se3-Se has seven stable sections, all of which are based on the ternary compound Cu3SbSe4. In the Cu-Sb-Sb2Se3-Cu2Se subsystem, 5 quasi-binary sections are stable: three based on binary Cu2Se and two sections based on ternary compounds CuSbSe2 and Cu3SbSe3.