BixSb2−xTe3 nanoplates with enhanced thermoelectric performance due to sufficiently decoupled electronic transport properties and strong wide-frequency phonon scatterings

Abstract

Thermoelectric materials enable the direct conversion between heat and electricity, offering a sustainable technology to overcome the upcoming energy crisis. p-Type BixSb2−xTe3 systems potentially satisfy the criteria (i.e. large power-factor, and low thermal conductivity) for thermoelectric applications. Nanostructuring has been considered as an effective approach to enhance the thermoelectric performance. Here, we employed a rapid microwave-assisted solvothermal method to fabricate BixSb2−xTe3 nanoplates, securing a peak figure-of-merit of 1.2, caused by the obtained high power-factor of 28.3×10−4Wm−1K−2 and ultra-low thermal conductivity of 0.7Wm−1K−1. Based on the single Kane band model with a newly introduced variable (λEdef — the dimensionless λ representing the square root of ratio between the initial effective mass and the free electron mass, and Edef representing the deformation potential) to serve as the decoupling factor, we found that BixSb2−xTe3 nanoplates with tunable compositions can decrease λEdef and simultaneously optimize the reduced Fermi level to ultimately enhance the power-factor. Moreover, detailed structural characterizations reveal dense grain boundaries and dislocations in our nanostructures. These two phonon scattering sources in conjunction with the inherently existed Bi–Sb lattice disorders lead to a strong wide-frequency phonon scattering, and consequently result in a significantly decreased thermal conductivity. This study provides strategic guidance to develop high-performance thermoelectric materials by nanostructuring and compositional engineering to achieve ultra-low thermal conductivity and to maximize the power-factor.