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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.


Related in: MedlinePlus

The Seebeck effect derived from different asymmetries of charge carriers at the Fermi level.(a) A conducting solid with a significant energy-dependent DOSs. (b) A junction of conducting solids A and B with different DOSs, which is the situation where the Seebeck effect was originally discovered. (c) A conducting solid with a steep energy dependence of the electron relaxation time τ. (d) A junction between two conducting solids of significantly different τ. The vertical axis denotes either N(ɛ) or τ(ɛ) at the Fermi level. The horizontal axis denotes temperature, or equivalently, the Fermi energy, due to their correlation. Note that scenarios c and d both produce a τ mismatch, which we exploit towards an enhanced Seebeck effect. When applying a magnetic field along the z direction, only in these two cases, transverse electric potential along the y direction (the Nernst effect) can be expected. In the case a and b, such a signal is fully compensated due to the Sondheimer cancellation (see text).
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f1: The Seebeck effect derived from different asymmetries of charge carriers at the Fermi level.(a) A conducting solid with a significant energy-dependent DOSs. (b) A junction of conducting solids A and B with different DOSs, which is the situation where the Seebeck effect was originally discovered. (c) A conducting solid with a steep energy dependence of the electron relaxation time τ. (d) A junction between two conducting solids of significantly different τ. The vertical axis denotes either N(ɛ) or τ(ɛ) at the Fermi level. The horizontal axis denotes temperature, or equivalently, the Fermi energy, due to their correlation. Note that scenarios c and d both produce a τ mismatch, which we exploit towards an enhanced Seebeck effect. When applying a magnetic field along the z direction, only in these two cases, transverse electric potential along the y direction (the Nernst effect) can be expected. In the case a and b, such a signal is fully compensated due to the Sondheimer cancellation (see text).

Mentions: The Seebeck coefficient of a conducting solid is generally induced by the asymmetry of the electronic density of states (DOSs) N(ɛ) at the Fermi level ɛF, as illustrated in Fig. 1a. There, a temperature gradient ΔTx along the sample leads to a slight gradient in the Fermi level ɛF (or, more generally, the chemical potential). Due to the energy dispersive N(ɛ) and the Fermi function f(ɛ), which both determine the charge-carrier density at ɛF, n(ɛF)=N(ɛF)f(ɛF), a net diffusion of electrons occurs along the sample. The electron diffusion is eventually impeded by a retarding electric potential (Vx), leading to SN=Vx//ΔTx/ at equilibrium. We denote this conventional contribution to the Seebeck effect as SN. From the thermodynamic point of view, this term measures the temperature derivative of ɛF per unit charge e, SN∝(1/e) ∂ɛF/∂T. It also explains Seebeck's original observation of an electric potential across the junction of two metallic wires (cf. Fig. 1b). Here the difference of the Fermi energies of the two metals simply sets up an artificial energy dependence of N(ɛ).


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 effect derived from different asymmetries of charge carriers at the Fermi level.(a) A conducting solid with a significant energy-dependent DOSs. (b) A junction of conducting solids A and B with different DOSs, which is the situation where the Seebeck effect was originally discovered. (c) A conducting solid with a steep energy dependence of the electron relaxation time τ. (d) A junction between two conducting solids of significantly different τ. The vertical axis denotes either N(ɛ) or τ(ɛ) at the Fermi level. The horizontal axis denotes temperature, or equivalently, the Fermi energy, due to their correlation. Note that scenarios c and d both produce a τ mismatch, which we exploit towards an enhanced Seebeck effect. When applying a magnetic field along the z direction, only in these two cases, transverse electric potential along the y direction (the Nernst effect) can be expected. In the case a and b, such a signal is fully compensated due to the Sondheimer cancellation (see text).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: The Seebeck effect derived from different asymmetries of charge carriers at the Fermi level.(a) A conducting solid with a significant energy-dependent DOSs. (b) A junction of conducting solids A and B with different DOSs, which is the situation where the Seebeck effect was originally discovered. (c) A conducting solid with a steep energy dependence of the electron relaxation time τ. (d) A junction between two conducting solids of significantly different τ. The vertical axis denotes either N(ɛ) or τ(ɛ) at the Fermi level. The horizontal axis denotes temperature, or equivalently, the Fermi energy, due to their correlation. Note that scenarios c and d both produce a τ mismatch, which we exploit towards an enhanced Seebeck effect. When applying a magnetic field along the z direction, only in these two cases, transverse electric potential along the y direction (the Nernst effect) can be expected. In the case a and b, such a signal is fully compensated due to the Sondheimer cancellation (see text).
Mentions: The Seebeck coefficient of a conducting solid is generally induced by the asymmetry of the electronic density of states (DOSs) N(ɛ) at the Fermi level ɛF, as illustrated in Fig. 1a. There, a temperature gradient ΔTx along the sample leads to a slight gradient in the Fermi level ɛF (or, more generally, the chemical potential). Due to the energy dispersive N(ɛ) and the Fermi function f(ɛ), which both determine the charge-carrier density at ɛF, n(ɛF)=N(ɛF)f(ɛF), a net diffusion of electrons occurs along the sample. The electron diffusion is eventually impeded by a retarding electric potential (Vx), leading to SN=Vx//ΔTx/ at equilibrium. We denote this conventional contribution to the Seebeck effect as SN. From the thermodynamic point of view, this term measures the temperature derivative of ɛF per unit charge e, SN∝(1/e) ∂ɛF/∂T. It also explains Seebeck's original observation of an electric potential across the junction of two metallic wires (cf. Fig. 1b). Here the difference of the Fermi energies of the two metals simply sets up an artificial energy dependence of N(ɛ).

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.


Related in: MedlinePlus