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 (𝜎 '(( ), thermal conductivity (𝑘 '(( ), and Seebeck coefficient (𝑆 '(( ) of composite materials made up of VO ) nanoparticles embedded in a Bi *.+ Sb ,.+ Te -(BST) matrix. The temperature evolution of these three properties along with the thermoelectric figure of merit (𝑍𝑇 = 𝜎 '(( 𝑆 '(( ) 𝑇 𝑘 '(( 7) is analyzed across the metal-insulator transition of VO ) and for temperatures up to 550 K. For temperatures higher than 350 K, it is shown that VO ) 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 VO ) nanoparticles provide an effective way to enhance the thermoelectric efficiency of Bi *.+ Sb ,.+ Tematerials. The calculated ZT values for VO ) are in good agreement with the experimental data reported in the literature for temperatures higher than 350 K. The thermal conductivity values obtained for VO ) 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 Bi *.+ Sb ,.+ Teand VO ) . Furthermore, the ratio 𝑘 '(( 𝑇𝜎 '(( ⁄ is found to be higher than the Lorenz number obtained for pure metals, such that its values increase with temperature and the VO ) concentration, for temperatures higher than the transition temperature (342.5 K) of VO ) .