In this work, p-type thermoelectric material was produced by hot extrusion of pre-synthesized in injection molding machine BixSb2-xTe3 ternary solid solution with x approximate to 0.4. Temperature dependences of its thermoelectric parameters were investigated in the range of 230-370 K. Extruded material exhibits a single phase of Bi-Sb-Te, about >97% relative density, electrical conductivity at about 1000 (Omega.cm)(-1) and the Seebeck coefficient at about 210 mu V/K at room temperature. Besides it is characterized by a significant heterogeneity of thermoelectric properties in its cross-section with spreadings of the Seebeck coefficient S +/- 2.5% and electrical conductivity sigma +/- 10%. Such heterogeneity correlates with stress-strain state nonuniformity that has been shown using mathematical modeling of the hot extrusion process. (c) 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Materials Science: Composites, Alloys and Materials Chemistry.

AbstractFor p -Bi_2Te_3 crystals grown by the Czochralski method, the temperature dependences of the conductivity, Hall coefficient, thermoelectric power (α), and transverse Nernst–Ettingshausen coefficient are obtained experimentally in the temperature range 77–450 K. The transmittance spectrum in the range 400–5250 cm^–1 is recorded at room temperature. It is shown that, to interpret the temperature dependences of the scattering parameter r and the ratio of the thermoelectric power to temperature (α/ T ), it is essential to take into account the complex valence-band structure and the contribution of heavy holes to transport phenomena. Estimations of the energy band parameters in the context of the two-band model give a hole effective mass close to the free electron mass and the energy gap between nonequivalent extrema at a level of several hundredths of eV. In the absorption spectrum derived from the transmittance spectrum, a sharp increase in absorption defined by indirect interband transitions with the band gap E _ g ≈ 0.14 eV is observed in the region of frequencies ν ≥ 1000 cm^–1. The absorption spectrum calculated from the reflectance data using the Kramers–Kronig relations is in agreement with the experimental absorption spectrum.

In this work, p-type thermoelectric material was produced by hot extrusion of pre-synthesized in injection molding machine Bi0.5Sb1.5Te3 solid solution. During the research radial distribution of the Seebeck coefficient was confirmed and described in material’s cross section using thermal measuring probe. Such nonuniformity of the Seebeck coefficient is correlated with the strain-stress state of extrudate specifically with the distribution of accumulated strain intensity, which was obtained by mathematical modeling of extrusion process using the software package DEFORM.

For p-Bi2Te3 crystals grown by the Czochralski method, the temperature dependences of the conductivity, Hall coefficient, thermoelectric power (α), and transverse Nernst–Ettingshausen coefficient are obtained experimentally in the temperature range 77–450 K. The transmittance spectrum in the range 400–5250 cm–1 is recorded at room temperature. It is shown that, to interpret the temperature dependences of the scattering parameter r and the ratio of the thermoelectric power to temperature (α/T), it is essential to take into account the complex valence-band structure and the contribution of heavy holes to transport phenomena. Estimations of the energy band parameters in the context of the two-band model give a hole effective mass close to the free electron mass and the energy gap between nonequivalent extrema at a level of several hundredths of eV. In the absorption spectrum derived from the transmittance spectrum, a sharp increase in absorption defined by indirect interband transitions with the band gap Eg ≈ 0.14 eV is observed in the region of frequencies ν ≥ 1000 cm–1. The absorption spectrum calculated from the reflectance data using the Kramers–Kronig relations is in agreement with the experimental absorption spectrum.