Approaches to Estimate the Magnitude of Phonon Scattering via Point Defects in Mo(Se_1-xTe_x)₂ Thermoelectric Alloys

One of the most popular routes used to improve the thermoelectric performance of materials is to suppress their lattice thermal conductivities. Thermoelectric performance is characterized by a figure-of-merit zT, which is defined as sigma(ST)-T-2/(kappa(e) + kappa(l)), where the sigma, S, T, kappa(e), and kappa(l) are the electrical conductivity, Seebeck coefficient, temperature (in Kelvin), electronic thermal conductivity, and the lattice thermal conductivity, respectively. Among the variables in zT, the kappa(l) is the only variable that is independent of all other variables. In other words, reduction in kappa(l) guarantees zT improvement. Therefore, several different strategies to decrease kappa(l) have been introduced and implemented. Among the many kappa(l) reduction strategies, introducing point defects in the material by forming an alloy is particularly effective. Here, phonon scattering due to point defects in Mo(Se1-xTex)(2) (x = 0.0, 0.25, 0.50, 0.75, 1.0) was studied using both the Debye-Callaway (DC) model and Callaway-von Baeyer (CvB) model. The advantages and disadvantages of using DC or CvB models are thoroughly discussed. When analyzing the effect of phonon scattering due to point defects, the CvB model is simpler and gives more information about the details of phonon scattering.