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.