Chapter 5 - Oxide thermoelectrics: a review and a case study

Abstract

Thermoelectric materials can make significant contributions to solve the global energy crises by converting waste heat into electricity and more efficient refrigeration based on the Seebeck and Peltier effects, respectively. The efficiency of conversion mainly depends on the figure of merit, which is based on the electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and lattice thermal conductivity. Many efforts have been done to improve the value of figure of merit using different approaches, such as nano-structuring, doping, molecular rattling, and nanocomposite formation. Recently, metal oxides attracted a great deal of interest for thermoelectric power generation at high temperature, Among these is SrTiO3, a promising thermoelectric material.This chapter first introduces thermoelectricity and then provides a brief history of thermoelectric materials. Next, it discusses the various approaches that have been employed to improve the value of figure of merit. Finally, it presents our experimental results on thermoelectric properties of niobium-doped SrTiO3. The polycrystalline samples of SrNb x Ti 1-x O 3 with x= 0.05, 0.10 and 0.15 have been synthesized by conventional solid-state reaction method to study systematic effect of Nb 5+ substitution on SrTiO 3. The phase purity investigated by X-ray diffraction, shows that all the three compounds are of single phase with a perovskite structure. The thermophysical properties, Seebeck coefficient, electrical and thermal conductivity have been measured from room temperature to 1000K. The Seebeck coefficient in all the three compounds is negative across the whole measured temperature range, proving the n-type conduction. It is found that a minimum of 15 % Ti-substitution with Nb is required to develop measurable electrical conductivity. The thermal conductivity of these samples was significantly reduced in the high-temperature region.