Effect of the Metal–Insulator Transition on the Thermoelectric Properties of Composites Based on Bi0.5Sb1.5Te3 with VO2 Nanoparticles
Résumé
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 (σeff), thermal conductivity (keff), and Seebeck coefficient (Seff) of composite materials made up of VO2 nanoparticles embedded in a Bi0.5Sb1.5Te3 (BST) matrix. The temperature evolution of these three properties along with the thermoelectric figure of merit (ZT=σeffS2effT/keff) is analyzed across the metal–insulator transition of VO2 and for temperatures up to 550 K. For temperatures higher than 350 K, it is shown that VO2 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 VO2 nanoparticles provide an effective way to enhance the thermoelectric efficiency of Bi0.5Sb1.5Te3 materials. The calculated ZT values for VO2 are in good agreement with the experimental data reported in the literature for temperatures higher than 350 K. The thermal conductivity values obtained for VO2 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 Bi0.5Sb1.5Te3 and VO2. Furthermore, the ratio keff/Tσeff is found to be higher than the Lorenz number for pure metals. Above the transition temperature of VO2 (342.5 K), this ratio increases with temperature and concentration, allowing to evaluate the role of electrons as energy carriers in these systems.
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