Improved thermoelectric performance in n-type BiTe facilitated by defect engineering

摘要

BiTe is a potentially attractive candidate for thermoelectric applications because it is the structural analogue of the state-of-the-art thermoelectric material,bismuth telluride(Bi_(2)Te_(3)). However, BiTe has attracted little attention due to its small band gap and high electron concentration. In this study, remarkable increase in thermoelectric performance in the n-type Bi_(1-x)Sb_(x)Te compounds through tuning the carrier concentration with chemical doping is shown. The Seebeck coefficient of Bi_(1-x)Sb_(x)Te increases remarkably while the electronic thermal conductivity decreases gradually as Sb content is increased, leading to enhanced thermoelectric figure of merit(ZT). Moreover, the simultaneous optimization of the electrical and thermal transport properties leads the peak temperature of the figure of merit to shift toward lower temperature with Sb content increasing in Bi_(1-x)Sb_(x)Te, thus making Bi_(1-x)Sb_(x)Te a potential alternative to bismuth telluride for near-room-temperature thermoelectric applications. In addition, the presence of multiple low-frequency optical phonons and their coupling with the long-wavelength heat carrying acoustic phonons in all the Bi_(1-x)Sb_(x)Te investigated are revealed based on the combined Debye-Einstein model. The present results provide the underlying mechanism connecting thermoelectric performance and lattice dynamics in Bi_(1-x)Sb_(x)Te compounds.