Pushing the optimal ZT values of p-type Bi2−xSbxTe3 alloys to a higher temperature by expanding band gaps and suppressing intrinsic excitation

Abstract

In this paper, the band gap and intrinsic excitation temperature of p-type Bi2−xSbxTe3 alloys were effectively adjusted by controlling antimony content. The higher the intrinsic excitation temperature was (higher the antimony content was), faster the electrical conductivity decreased with temperature, and the Seebeck coefficient peaks also occurred at a higher temperature. In addition, the effect of ambipolar thermal conductivity could not be ignored when the temperature is over the intrinsic excitation temperature. The starting temperature of ambipolar thermal conductivity increased from 320 to 380 K with x from 1.52 to 1.64 for Bi2−xSbxTe3 alloys, and meanwhile the contribution of the ambipolar thermal conductivity to the total thermal conductivity was also becoming smaller and smaller. As a result, the corresponding optimal peaks of the figure of merits (ZT) were pushed to a higher temperature with increasing antimony contents. The sample of Bi0.44Sb1.56Te3 obtained the maximum ZT value of 1.22 at 340 K, and the mean ZT values of Bi0.4Sb1.6Te3 and Bi0.44Sb1.56Te3 were all over 1.0 in a wide range of temperature from 300 to 460 K, which would be very suitable for the low temperature thermoelectric power generation.