Investigation of the Thermoelectric Performance of PbTe-Ag2Se Derived Pseudo-solid Solutions, Nanostructures and Nano-composites

Clemson University, Clemson SC

Investigators

Abstract

TECHNICAL SUMMARY: This project investigates structure formation and electrical and thermal transport properties of PbTe-Ag2-äSe alloys. Solid-solutions of PbTe-Ag2-äSe display extremely interesting structural behavior, low electrical resistivity and very low thermal conductivity. Hence, this system has the potential to give rise to a new state-of ?the-art thermoelectric material for power generation applications. In addition to the favorable transport properties exhibited by the system, the resulting alloys are stable and mechanically robust thus allowing excessive manipulation for optimization of the thermoelectric performance. It has been observed that dense solid-solutions of PbTe-Ag2-äSe (1:1 molar ratio) result in a predominantly single phase alloy which crystallizes in the NaCl structure. Stabilization of a predominantly cubic single phase alloy in the presence of such a high level of structural disorder is remarkable. PbTe appears to dictate structure formation from the melt and not Ag2Se - which stabilizes in an orthorhombic structure at low temperatures and cubic at high temperatures. The PbTe-Ag2-äSe alloys are degenerate semiconductors whose electrical transport correlates with Ag concentration. Preliminary measurements on several samples with ä = 0.1 showed p-type behavior and a high-temperature (~ 400 oC) total thermal-conductivity value êT< 0.6 W/m-K. This work will investigate the structure formation of these alloys using x-ray diffraction and microscopy, and study the effects of structure manipulation, i.e. further alloying, nano-structuring and nano-composites, on the thermoelectric properties. This research will provide excellent training for graduate and undergraduate students in material synthesis and characterization. NON-TECHNICAL SUMMARY: This proposal will utilize solid-solutions, nano-structuring and band-gap engineering in order to obtain a high efficiency thermoelectric alloy for power generation applications. Development of thermoelectric materials for power generation is an essential component in our scientific effort to achieve energy independence and security. Thermoelectric materials convert wasted heat to electricity, which implies that any heat source, either man-made (automotives) or natural (hot springs) can be utilized for production of electrical energy. The presence of a temperature gradient across the thermoelectric will give rise to a voltage. Thermoelectric materials also offer the mechanical advantage of absence of moving parts, which eliminates the need for lubrication and frequent maintenance. This work will research the structure formation and high temperature thermoelectric performance of PbTe-Ag2-äSe alloys. These alloys have been shown to have very low thermal conductivity and good electrical conductivity. Both are needed in order to obtain an efficient thermoelectric material. Additionally, the high temperature thermoelectric performance will be optimized through the chemical and mechanical processing of these alloys. This research will provide excellent training for graduate and undergraduate students in material synthesis and characterization. One graduate student and two undergraduate students will be working on this project and will be involved in all aspects of this investigation. The PI actively encourages the participation of women and minorities in his research.