Counterintuitive example on relation between ZT and thermoelectric efficiency

The thermoelectric figure of merit ZT, which is defined using electrical conductivity, Seebeck coefficient, thermal conductivity, and absolute temperature T, has been widely used as a simple estimator of the conversion efficiency of a thermoelectric heat engine. When material properties are constant...

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Bibliographic Details
Published in:Applied physics letters 2020-05, Vol.116 (19)
Main Authors: Ryu, Byungki, Chung, Jaywan, Choi, Eun-Ae, Ziolkowski, Pawel, Müller, Eckhard, Park, SuDong
Format: Article
Language:English
Subjects:
Applied physics
Conversion
Efficiency
Electrical resistivity
Figure of merit
Heat engines
Material properties
Operating temperature
Seebeck effect
Temperature
Thermal conductivity
Thermoelectric materials
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Summary:The thermoelectric figure of merit ZT, which is defined using electrical conductivity, Seebeck coefficient, thermal conductivity, and absolute temperature T, has been widely used as a simple estimator of the conversion efficiency of a thermoelectric heat engine. When material properties are constant or slowly varying with T, a higher ZT ensures a higher maximum conversion efficiency of thermoelectric materials. However, as material properties can vary strongly with T, efficiency predictions based on ZT can be inaccurate, especially for wide-temperature applications. Moreover, although ZT values continue to increase, there has been no investigation of the relationship between ZT and the efficiency in the higher ZT regime. In this paper, we report a counterintuitive situation by comparing two materials: although one material has a higher ZT value over the whole operating temperature range, its maximum conversion efficiency is smaller than that of the other. This indicates that, for material comparisons, the evaluation of exact efficiencies as opposed to a simple comparison of ZTs is necessary in certain cases.
ISSN:0003-6951
1077-3118
DOI:10.1063/5.0003749