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Large Seebeck effect by charge-mobility engineering.

Sun P, Wei B, Zhang J, Tomczak JM, Strydom AM, Søndergaard M, Iversen BB, Steglich F - Nat Commun (2015)

Bottom Line: Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient.Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch.When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

No MeSH data available.


The Seebeck coefficient S(T) of Co0.999Ni0.001Sb3.The measured S(T) is compared with calculated values of −ν/μH, that is, the expected Seebeck contribution, Sτ, derived from the mobility gradient, see text. Note that the positive peak developed below 50 K due to the n-type charge carriers can be well reproduced by this ratio. The hatched area indicates the temperature window where two electron-like bands are involved, and these cannot describe the occurrence of the positive S(T) peak.
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f2: The Seebeck coefficient S(T) of Co0.999Ni0.001Sb3.The measured S(T) is compared with calculated values of −ν/μH, that is, the expected Seebeck contribution, Sτ, derived from the mobility gradient, see text. Note that the positive peak developed below 50 K due to the n-type charge carriers can be well reproduced by this ratio. The hatched area indicates the temperature window where two electron-like bands are involved, and these cannot describe the occurrence of the positive S(T) peak.

Mentions: Next, we will demonstrate the pivotal influence of the above mechanism for a weakly Ni-doped skutterudite CoSb3. As shown in Fig. 2 (see also ref. 12), S(T) of Co0.999Ni0.001Sb3 is negative and only weakly temperature dependent above 50 K. Further cooling of the temperature leads to a marked sign change of S(T) and a pronounced positive peak of 110 μV K−1 at T≈20 K. Here we highlight the opposite signs of S(T) and RH(T) below 30 K, the latter being negative in the whole temperature range investigated (cf. Fig. 3a). Phonon-drag effects are unlikely to play the key role in the origin of the extraordinary S(T) peak at 20 K due to its absence in undoped CoSb3 and its sensitivity to slight change in Ni concentration12. In view of the opposite signs of S(T) and RH(T) and to account for the unusual peak in the former, an intuitive approach involves a two-band model, with charge carriers of different signs being involved. This is, however, in contradiction to the Hall resistivity data that hint to two electron-like bands (cf. Supplementary Fig. 1 and Supplementary Note 1), whose influences furthermore only coexist in a very limited temperature region (25−40 K, hatched in Fig. 2). Near 20 K, the one-band nature is restored. These observations imply that, while two-band effects are involved in a limited temperature interval (cf. Figs 2 and 3a), they are not responsible for the positive S(T) peak. Another likely multiband regime below T≈7 K (cf. Fig. 3a) is beyond the scope of this investigation. In view of the sublinear ρH(B) above 10 K, we proceed our discussion in the framework of a one-band picture. This applies at least to the low magnetic field region (B≤2 T) where we have measured ν(T) and estimated RH(T).


Large Seebeck effect by charge-mobility engineering.

Sun P, Wei B, Zhang J, Tomczak JM, Strydom AM, Søndergaard M, Iversen BB, Steglich F - Nat Commun (2015)

The Seebeck coefficient S(T) of Co0.999Ni0.001Sb3.The measured S(T) is compared with calculated values of −ν/μH, that is, the expected Seebeck contribution, Sτ, derived from the mobility gradient, see text. Note that the positive peak developed below 50 K due to the n-type charge carriers can be well reproduced by this ratio. The hatched area indicates the temperature window where two electron-like bands are involved, and these cannot describe the occurrence of the positive S(T) peak.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4491185&req=5

f2: The Seebeck coefficient S(T) of Co0.999Ni0.001Sb3.The measured S(T) is compared with calculated values of −ν/μH, that is, the expected Seebeck contribution, Sτ, derived from the mobility gradient, see text. Note that the positive peak developed below 50 K due to the n-type charge carriers can be well reproduced by this ratio. The hatched area indicates the temperature window where two electron-like bands are involved, and these cannot describe the occurrence of the positive S(T) peak.
Mentions: Next, we will demonstrate the pivotal influence of the above mechanism for a weakly Ni-doped skutterudite CoSb3. As shown in Fig. 2 (see also ref. 12), S(T) of Co0.999Ni0.001Sb3 is negative and only weakly temperature dependent above 50 K. Further cooling of the temperature leads to a marked sign change of S(T) and a pronounced positive peak of 110 μV K−1 at T≈20 K. Here we highlight the opposite signs of S(T) and RH(T) below 30 K, the latter being negative in the whole temperature range investigated (cf. Fig. 3a). Phonon-drag effects are unlikely to play the key role in the origin of the extraordinary S(T) peak at 20 K due to its absence in undoped CoSb3 and its sensitivity to slight change in Ni concentration12. In view of the opposite signs of S(T) and RH(T) and to account for the unusual peak in the former, an intuitive approach involves a two-band model, with charge carriers of different signs being involved. This is, however, in contradiction to the Hall resistivity data that hint to two electron-like bands (cf. Supplementary Fig. 1 and Supplementary Note 1), whose influences furthermore only coexist in a very limited temperature region (25−40 K, hatched in Fig. 2). Near 20 K, the one-band nature is restored. These observations imply that, while two-band effects are involved in a limited temperature interval (cf. Figs 2 and 3a), they are not responsible for the positive S(T) peak. Another likely multiband regime below T≈7 K (cf. Fig. 3a) is beyond the scope of this investigation. In view of the sublinear ρH(B) above 10 K, we proceed our discussion in the framework of a one-band picture. This applies at least to the low magnetic field region (B≤2 T) where we have measured ν(T) and estimated RH(T).

Bottom Line: Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient.Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch.When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

No MeSH data available.