The Thermoelectric Figure of Merit and its Relation to Thermoelectric Generators†

Chasmar, R. P.; Stratton, R.

doi:10.1080/00207215908937186

Cited by 326 publications

(221 citation statements)

References 7 publications

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“…To reveal the electronic origins of the observed superior TE performance of GeTe, it is known that the maximal power factor is proportional to the number of degenerated band valleys (N v ) and inversely proportional to the inertial mass (m I *) of each valley (PF∝μm *3/2 ∝N v /m I *) when the scattering of carriers is dominated by acoustic phonons, 26,82,84,85 as is the case in the group IV monotellurides studied here. This indicates that a large N v and a small m I * are beneficial for TE s.…”

Section: Resultsmentioning

confidence: 99%

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

et al. 2017

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PbTe and SnTe in their p-type forms have long been considered high-performance thermoelectrics, and both of them largely rely on two valence bands (the first band at L point and the second one along the Σ line) participating in the transport properties. This work focuses on the thermoelectric transport properties inherent to p-type GeTe, a member of the group IV monotellurides that is relatively less studied. Approximately 50 GeTe samples have been synthesized with different carrier concentrations spanning from 1 to 20 × 10 20 cm − 3 , enabling an insightful understanding of the electronic transport and a full carrier concentration optimization for the thermoelectric performance. When all of these three monotellurides (PbTe, SnTe and GeTe) are fully optimized in their p-type forms, GeTe shows the highest thermoelectric figure of merit (zT up to 1.8). This is due to its superior electronic performance, originating from the highly degenerated Σ band at the band edge in the low-temperature rhombohedral phase and the smallest effective masses for both the L and Σ bands in the high-temperature cubic phase. The high thermoelectric performance of GeTe that is induced by its unique electronic structure not only provides a reference substance for understanding existing research on GeTe but also opens new possibilities for the further improvement of the thermoelectric performance of this material.

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Section: Resultsmentioning

confidence: 99%

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

et al. 2017

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Section: Introductionmentioning

confidence: 99%

“…1,2 However, the thermoelectric power factor, which characterizes the electrical properties, is known to be a function of effective mass (m*) and mobility (m) 1,3-5 via the weighted mobility 3,4,6,7 (S 2 /r f m* 1.5 m). A further consideration of multi-valley band systems and carrier scattering by acoustic vibrations, [8][9][10] as found in most efficient thermoelectrics at temperatures where zT peaks, reveals that large number of valleys (N v ) 3,4,11,12 and low conduction mass (m c *) are beneficial for thermoelectric performance (S 2 /r f N v /m c *). 3,4,[13][14][15] In spite of the low degeneracy, it has long been known that narrow band gap G-semiconductors (N v ¼ 1) such as InSb and InAs contain a power factor as high or even higher 16,17 than those of known high degeneracy n-type thermoelectrics 18 (N v $ 4), because of the extremely low effective masses (#0.05m e , where m e is the free electron mass).…”

Section: Introductionmentioning

confidence: 99%

“…A further consideration of multi-valley band systems and carrier scattering by acoustic vibrations, [8][9][10] as found in most efficient thermoelectrics at temperatures where zT peaks, reveals that large number of valleys (N v ) 3,4,11,12 and low conduction mass (m c *) are beneficial for thermoelectric performance (S 2 /r f N v /m c *). 3,4,[13][14][15] In spite of the low degeneracy, it has long been known that narrow band gap G-semiconductors (N v ¼ 1) such as InSb and InAs contain a power factor as high or even higher 16,17 than those of known high degeneracy n-type thermoelectrics 18 (N v $ 4), because of the extremely low effective masses (#0.05m e , where m e is the free electron mass). 19 However, very few studies have shown zT > 0.5 in these materials, because of the strong detrimental effects of minority carriers due to the small gap and/or the high thermal conductivity 16,20 ($20 W m À1 K À1 at 300 K).…”

Section: Introductionmentioning

confidence: 99%

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Alloying to increase the band gap for improving thermoelectric properties of Ag2Te

2011

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Ag 2 Te simultaneously shows high mobility and low thermal conductivity, however the relatively low band gap of $0.2 eV prevents it from achieving high thermoelectric figure of merit, zT, in the high temperature phase. In this study, the band gap of Ag 2 Te has been increased enabling a zT of unity by forming alloys and composites with PbTe, thereby demonstrating the importance of exploiting potentially good thermoelectrics among these small band gap semiconductors and similar materials.

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“…determines the optimized figure of merit (14)(15)(16) (N V is the band degeneracy, m Ã b is the density of states effective mass of a single band, μ 0 is the mobility at nondegenerate limit, and κ L is the lattice thermal conductivity). This expression is derived for semiconductors with single band transport behavior where the carrier concentration can be optimized to achieve maximum zT.…”

mentioning

confidence: 99%

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

Wang

Pei

LaLonde

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

390

365

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PbSe is a surprisingly good thermoelectric material due, in part, to its low thermal conductivity that had been overestimated in earlier measurements. The thermoelectric figure of merit, zT, can exceed 1 at high temperatures in both p-type and n-type PbSe, similar to that found in PbTe. While the p-type lead chalcogenides (PbSe and PbTe) benefit from the high valley degeneracy (12 or more at high temperature) of the valence band, the n-type versions are limited to a valley degeneracy of 4 in the conduction band. Yet the n-type lead chalcogenides achieve a zT nearly as high as the p-type lead chalcogenides. This effect can be attributed to the weaker electron-phonon coupling (lower deformation potential coefficient) in the conduction band as compared with that in the valence band, which leads to higher mobility of electrons compared to that of holes. This study of PbSe illustrates the importance of the deformation potential coefficient of the charge-carrying band as one of several key parameters to consider for band structure engineering and the search for high performance thermoelectric materials.energy | semiconductor | quality factor W aste heat recovery using thermoelectric power generation is attracting considerable interest from the automobile industry (1) as well as from many other areas (2). Large-scale production of bulk materials with high figure of merit, zT, defined as zT ¼ S 2 σT∕ðκ e þ κ L Þ (S is the Seebeck coefficient, σ is the electric conductivity, and κ e and κ L are the electronic and lattice thermal conductivity, respectively), is the key to widespread adaption of thermoelectric technology. The search for good thermoelectric materials has focused on investigating semiconductors that have suitable band structures and low thermal conductivities (3, 4). As one of the first investigated material systems (5), PbTe and its alloys have been extensively studied and remain some of the best (6, 7) thermoelectric materials for applications from 500 to 900 K. Considerable effort has been made to achieve a higher zT in these alloys by reducing the lattice thermal conductivity, κ L , by incorporation of nanometer scale inclusions (8-11). Other strategies approach the challenge of increasing zT from different angles, such as band structure distortion by Tl doping (12), and more recently, increasing band degeneracy by converging two different valence bands in p-type PbTe (13).It can be shown that the material parameter called the thermoelectric quality factor, B,determines the optimized figure of merit (14-16) (N V is the band degeneracy, m Ã b is the density of states effective mass of a single band, μ 0 is the mobility at nondegenerate limit, and κ L is the lattice thermal conductivity). This expression is derived for semiconductors with single band transport behavior where the carrier concentration can be optimized to achieve maximum zT. For good thermoelectric semiconductors the dominant scattering mechanism at high temperatures, where zT peaks, is typically due to acoustic phonons. The deformation pote...

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The Thermoelectric Figure of Merit and its Relation to Thermoelectric Generators†

Cited by 326 publications

References 7 publications

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

Alloying to increase the band gap for improving thermoelectric properties of Ag2Te

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

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