TITLE:
Structure and Thermoelectric Properties of Nanostructured (Bi, Sb)2Te3 (Review)
AUTHORS:
Igor A. Drabkin, Vladimir V. Karataev, Vladimir B. Osvenski, Aleksandr I. Sorokin, Gennady I. Pivovarov, Natalie Yu. Tabachkova
KEYWORDS:
Solid Solutions (Bi, Sb)2Te3 P-Type; Nanostructure; Spark Plasma Sintering; Conductivity; Hall Effect; Hole Free Path; Seebeck Coefficient; Thermal Conductivity; Figure of Merit
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.3 No.2,
June
5,
2013
ABSTRACT:
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 Ts = 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 Ts increases
so that no broadening of X-ray lines at Ts = 400°C can take place. At higher Ts, 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 Bi0.5Sb1.5Te3 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 Bi0.4Sb1.6Te3 at Ts = 500°C and a pressure of 50
MPa. The causes of an apparent increase in thermoelectric efficiency are discussed.