Effect of the Metal–Insulator Transition on the Thermoelectric Properties of Composites Based on ${\mathrm{Bi}}_{0.5}{\mathrm{Sb}}_{1.5}{\mathrm{Te}}_{3}$ with ${\mathrm{VO}}_{2}$ Nanoparticles

Abstract

Bismuth telluride-based materials have been widely investigated due to their applications for the development of high-performance thermoelectric devices. Here, we numerically determine the effective electrical conductivity (${\sigma }_{eff}$), thermal conductivity (${k}_{eff}$), and Seebeck coefficient (${S}_{eff}$) of composite materials made up of ${\mathrm{VO}}_{2}$ nanoparticles embedded in a ${\mathrm{Bi}}_{0.5}{\mathrm{Sb}}_{1.5}{\mathrm{Te}}_{3}$ (BST) matrix. The temperature evolution of these three properties along with the thermoelectric figure of merit ($ZT={\sigma }_{eff}{S}_{eff}^{2}T/{k}_{eff}$) is analyzed across the metal–insulator transition of ${\mathrm{VO}}_{2}$ and for temperatures up to 550 K. For temperatures higher than 350 K, it is shown that ${\mathrm{VO}}_{2}$ nanoparticles with a concentration of 34 % enhance the electrical conductivity and ZT of the matrix by about 16 % and 10 %, respectively, while the Seebeck coefficient remains pretty much constant. This indicates that ${\mathrm{VO}}_{2}$ nanoparticles provide an effective way to enhance the thermoelectric efficiency of ${\mathrm{Bi}}_{0.5}{\mathrm{Sb}}_{1.5}{\mathrm{Te}}_{3}$ materials. The calculated ZT values for ${\mathrm{VO}}_{2}$ are in good agreement with the experimental data reported in the literature for temperatures higher than 350 K. The thermal conductivity values obtained for ${\mathrm{VO}}_{2}$ in the insulating phase are in good agreement with the experimental data reported in the literature, which are used to calculate the interface thermal resistance between ${\mathrm{Bi}}_{0.5}{\mathrm{Sb}}_{1.5}{\mathrm{Te}}_{3}$ and ${\mathrm{VO}}_{2}$. Furthermore, the ratio ${k}_{eff}/T{\sigma }_{eff}$ is found to be higher than the Lorenz number for pure metals. Above the transition temperature of ${\mathrm{VO}}_{2}$ (342.5 K), this ratio increases with temperature and concentration, allowing to evaluate the role of electrons as energy carriers in these systems.