Mechanical and Thermoelectric Properties of Solid Solutions of Bismuth and Antimony Chalcogenides Depending on the Purity of Initial Materials

The influence of the purity of the initial components on the mechanical and thermoelectric properties of extruded samples based on Sb₂Te₃–Bi₂Te₃ (p-type conductivity) and Bi₂Te₃–Bi₂Se₃ (n-type conductivity) solid solutions is studied. Powders of materials (with a purity of 99.99, 99.999, and 99.9999 wt % of the main substance) obtained by rapid crystallization of the melt in water or by grinding ingots fused in an ampoule are used. The samples are finely crystalline, the grain sizes do not exceed 10 μm, and materials with p-type conductivity contain inclusions of the second phase (tellurium-based eutectics). The mechanical and thermoelectric properties are determined; the ultimate strength during compressive deformation at room temperature of these samples is 170 ± 20 MPa for material with p-type conductivity and 241 ± 17 MPa for material with n-type conductivity. The thermoelectric parameters (electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit) of samples are measured in the range from 100 to 600 K. The purity of initial components does not have a significant effect on the thermoelectric figure of merit (ZT) of samples with p-type conductivity. For samples with n-type conductivity obtained from the purest materials, the maximum of thermoelectric figure of merit ZT is shifted towards higher temperatures. The maximum thermoelectric figure of merit is ZT_max ~ 1.1 at 340 K for material with p-type conductivity and ZT_max ~ 1.0 at 420 K for material with n-type conductivity.