First-Principles Estimation of Seebeck Coefficient of Bismuth Telluride and Selenide

The first-principles electronic band structure calculation has been used to examine the relationship between the Bi/Sb composition ratio and the Seebeck coefficient in (Bi1-x Sb x )2Te3. The Te/Se ratio dependence in Bi2(Te1-x Se x )3 has also been investigated and the results have been compared. Because spin–orbit interaction affects the band structure to a large extent, its inclusion is crucial to a quantitative discussion on the Seebeck coefficient. We have found that the Bi/Sb or Te/Se ratio does not have a large effect on the Seebeck coefficient. However, carrier density largely influences the temperature dependence of the Seebeck coefficient. Both the p- and n-type of thermoelectric materials were examined and the results show that their stabilities have the same tendency. The carrier densities in them are largely associated with defects, which suggests that a careful defect control is very important in the production process.