MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Material Dependence of the Thermoelectric Figure of Merit
Yukari Katsura
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2016 Volume 57 Issue 7 Pages 1035-1039

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Abstract

First-principles calculations were used to perform a cross-material investigation on the electronic structures of 13 parent compounds for thermoelectric materials. Boltzmann transport equations were used to calculate carrier doping level dependence of the Seebeck coefficient, electrical conductivity with respect to relaxation time, effective Lorenz numbers and the maximum possible thermoelectric figure of merit (ZeT) in the limit of zero phonon thermal conductivity. High ZeT was obtained only in semiconductors with finite band gaps. High ZeT for high doping level was achieved in compounds that had a steep density of states at the band edge. Calculations were combined with experimental transport properties to evaluate electron relaxation time of the samples. These analyses can be used to understand the nature of electron scattering mechanisms in specific thermoelectric materials and reduce the number of experiments required to develop new thermoelectric materials.

Fig. 1 (a) DOS of the 12 thermoelectric material parent compounds, normalized by unit cell volume. TB–mBJ was employed as the exchange-correlation potential. One grid along the vertical axes corresponds to normalized DOS of 1030 eVm−3. The letters in parentheses indicate the selected carrier types used for the transport calculations. (b) n-dependence of the absolute Seebeck coefficients at 300 K. (c) n-dependence of electrical conductivity (σ) divided by τel. (d) n-dependence of effective Lorenz number. The black line indicates the theoretical value L0 obtained from the free electron model. (e), (f) n-dependence of ZeT at (e) 300 K and (f) 900 K, assuming rigid crystal structures. (g) n-dependence of ZT at 900 K, assuming that κph/τel decreased to 1014 Wm−1K−1s−2 in all materials. Fullsize Image
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© 2016 The Japan Institute of Metals and Materials
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