Investigation of the Thermoelectric Properties of Single and Double Substituted Cu12Sb4S13 Tetrahedrite

Abstract

According to the current energy consumption, out of the total energy supplied as input in various sources such as power plants, factories, automobiles, etc., only around 30% of the energy is converted to useful work. The rest, about 70% of the energy is wasted, of which, waste heat is a major component. We can use thermoelectric generators (TEGs) to capture this waste heat and convert back into useful electrical energy. Moreover, TEGs can be used as alternate sources of electrical energy which would also help in reducing the carbon footprint. However, the current state of the art materials used in such TEGs are composed of toxic or costly elements. In this context, Tetrahedrite with nominal composition of Cu12Sb4S13, is a potential candidate containing relatively abundant, non-toxic (Cu and S), environment friendly elements, that can be suited for thermoelectric applications in the mid-temperature range (500 – 700 K). The pristine Cu12Sb4S13 tetrahedrite exhibits a fairly high figure of merit (zT) of 0.7 at 673 K, primarily due to its intrinsically low thermal conductivity. In this thesis, we have performed single and double substitutions at Cu, Sb and S sites in Cu12Sb4S13 that enabled us to simultaneously optimize the power factor and thermal conductivity, resulting in an enhancement of zT. The thesis first introduces a brief history and evolution of thermoelectric research, followed by an explanation of the various thermoelectric effects. The thermoelectric performance and conversion efficiency of a material are discussed in terms of dimensionless figure of merit (zT). This is followed by a review of the various transport properties such as electrical conductivity, Seebeck coefficient and thermal conductivity governing the zT of a material. A detailed literature survey of the tetrahedrite (Cu12Sb4S13) material is presented and the motivation for the work done in the thesis is given. The various experimental techniques and theoretical calculations (using density functional theory) followed in the thesis are also discussed