Investigation on Ternary Metal Chalcogenides for Intermediate Temperature Thermoelectric Applications

Abstract

This thesis explores the feasibility and possibility of promoting the ternary transition metal chalcogenides as low-cost and eco-friendly thermoelectric materials based on the Seebeck effect. In this context, thermoelectric (TE) technology has been considered an effective renewable technology as it transforms waste heat into useful electricity. As the conversion efficiency is directly coupled with the material s thermoelectric figure of merit, zT, an increase in zT can enhance the efficiency, which is indeed a challenging task because of the interdependency nature between TE parameters. Though some of the materials exhibit notably large zT such as SnSe, PbTe, GeTe, and (BiSb)2Te3, most are expensive and toxic. Consequently, the search for a new class of low-cost, high-zT materials remains an open challenge for the TE community. The efficiency (zT) of a material depends on the three transport parameters: electrical conductivity (and#963;), Seebeck coefficient (S), and total thermal conductivity (and#954;total) at absolute temperature (T), which influence the choice of an ideal thermoelectric material. Furthermore, the difficulty in developing thermoelectric materials with high zT derives from the significant correlation between the S, and#963;, and and#954;total that is, dependent on the carrier concentration n .The state-of-art thermoelectric materials, such as Bi2Te3, PbTe and GeTe, have shown high zT values. Specifically, a high zT of 2.62 is achieved in a single crystal of SnSe and similarly, a high zT of 1.86 ± 0.15 at 320 K is achieved for the composition of Bi0.5Sb1.5Te3. Interestingly, eco-friendly and low-cost materials, such as chalcogenides (AgSbSe2, CuInSe2, Cu2Se), silicides (HMS), antimonides (InSb,ZnSb), etc., have also shown a high zT value, where most of them are still toxic and lack temperature stability and in some case the thermal conductivity is very high newline