Author(s)

Igor A. Drabkin, Vladimir V. Karataev, Vladimir B. Osvenski, Aleksandr I. Sorokin, Gennady I. Pivovarov, Natalie Yu. Tabachkova

Department of dielectric and semiconductor materials, National University of Science and Technology “MISIS”, Moscow, Russia.
Department of functional and structural materials, Technological Institute of Superhard and New Carbon Materials, Troitsk, Russia.
Department of semiconductor materials, Giredmet Ltd., Moscow, Russia.

The investigation of the structure and thermoelectric properties of nanostructured solid solutions (Bi, Sb)₂Te₃ p-type has been carried out. The samples were obtained by grinding of original compositions in a planetary ball mill and by spark plasma sintering (SPS). Initial powder has an average particle size of 10 - 12 nm according to transmission electron microscopy, and the size of the coherent scattering region (CSR) obtained by X-ray line broadening. During sintering at T_s = 250°C - 400°C, the grain size and CSR increased, which was associated with the processes of recrystallization. The maximum of size distribution of CSR shifts to larger sizes when T_s increases so that no broadening of X-ray lines at T_s = 400°C can take place. At higher T_s, the emergence of new nanograins is observed. The formation of nanograins is conditioned by reducing of quantity of the intrinsic point defects produced in the grinding of the source materials. The study of the electrical conductivity and the Hall effect in a single crystal allows to estimate the mean free path of the holes-L in the single crystal Bi_0.5Sb_1.5Te₃ which at room temperature is 2 - 5 nm (it is much smaller than the dimensions of CSR in the samples). The method for evaluation of L in polycrystalline samples is proposed. At room temperature, L is close to the mean free path in single crystals. Scattering parameter holes in SPS samples obtained from the temperature dependence of the Seebeck coefficient are within the measurement error equal to the parameter of the scattering of holes in a single crystal. The figure of merit ZT of SPS samples as a function of composition and sintering temperature has been investigated. Maximum ZT, equal to 1.05 at room temperature, is obtained for the composition Bi_0.4Sb_1.6Te₃ at T_s = 500°C and a pressure of 50 MPa. The causes of an apparent increase in thermoelectric efficiency are discussed.

Solid Solutions (Bi, Sb)2Te3 P-Type; Nanostructure; Spark Plasma Sintering; Conductivity; Hall Effect; Hole Free Path; Seebeck Coefficient; Thermal Conductivity; Figure of Merit

I. Drabkin, V. Karataev, V. Osvenski, A. Sorokin, G. Pivovarov and N. Tabachkova, "Structure and Thermoelectric Properties of Nanostructured (Bi, Sb)₂Te₃ (Review)," Advances in Materials Physics and Chemistry, Vol. 3 No. 2, 2013, pp. 119-132. doi: 10.4236/ampc.2013.32018.