Phase transition enhanced thermoelectric figure-of-merit in copper chalcogenides

David R Brown,G Jeffrey Snyder,Tristan Day,Kasper A Borup,Bo B Iversen,Sebastian Christensen

doi:10.1063/1.4827595

David R Brown, G Jeffrey Snyder + Show 4 more

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https://doi.org/10.1063/1.4827595

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Abstract

While thermoelectric materials can be used for solid state cooling, waste heat recovery, and solar electricity generation, low values of the thermoelectric figure of merit, zT, have led to an efficiency too low for widespread use. Thermoelectric effects are characterized by the Seebeck coefficient or thermopower, which is related to the entropy associated with charge transport. For example, coupling spin entropy with the presence of charge carriers has enabled the enhancement of zT in cobalt oxides. We demonstrate that the coupling of a continuous phase transition to carrier transport in Cu2Se over a broad (360–410 K) temperature range results in a dramatic peak in thermopower, an increase in phonon and electron scattering, and a corresponding doubling of zT (to 0.7 at 406 K), and a similar but larger increase over a wider temperature range in the zT of Cu1.97Ag.03Se (almost 1.0 at 400 K). The use of structural entropy for enhanced thermopower could lead to new engineering approaches for thermoelectric materials with high zT and new green applications for thermoelectrics.

Highlights

Thermoelectric generators are solid state heat engines
While a vapor compression heat engine, such as a steam engine, extracts useful energy from the cycle of a fluid’s entropy change with temperature, a thermoelectric device utilizes an analogous cycle with a charged fluid.[1]
Following Emin,[6] we refer to the first term as the “transport thermopower,” αtransport, and the second term as the presence thermopower, αpresence

Summary

Introduction

Thermoelectric generators are solid state heat engines. While a vapor compression heat engine, such as a steam engine, extracts useful energy from the cycle of a fluid’s entropy change with temperature, a thermoelectric device utilizes an analogous cycle with a charged fluid (electrons in a solid semiconductor).[1]. We consider coupling the carrier transport to degrees of freedom associated with the structural changes of a phase transition.

Results

Conclusion