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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 Nernst coefficient of Co0.999Ni0.001Sb3.The green solid line represents ATdμH/dT, the expected contribution to ν(T) from the marked charge mobility change (cf. equation (1)), where the prefactor A=−(π2/3) kB//e/. The quantitative agreement found below 40 K between this calculation and the measured Nernst coefficient (black symbols) lends strong evidence that the enhanced Nernst signal originates from the significant mobility mismatch across the sample. The red dashed line displays the Hall mobility μH(T). ν(T) is expected to approximately scale with μH(T) assuming a weak temperature dependence of the latter, which indeed holds above 40 K (see text for details).
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f4: The Nernst coefficient of Co0.999Ni0.001Sb3.The green solid line represents ATdμH/dT, the expected contribution to ν(T) from the marked charge mobility change (cf. equation (1)), where the prefactor A=−(π2/3) kB//e/. The quantitative agreement found below 40 K between this calculation and the measured Nernst coefficient (black symbols) lends strong evidence that the enhanced Nernst signal originates from the significant mobility mismatch across the sample. The red dashed line displays the Hall mobility μH(T). ν(T) is expected to approximately scale with μH(T) assuming a weak temperature dependence of the latter, which indeed holds above 40 K (see text for details).

Mentions: Here the energy derivative of the tangent of the Hall angle can be expressed by using either μH or τ because tanθH=eBτ/m*=μHB, where m* denotes the effective mass of the relevant charge carriers. Apparently, ν is sensitive to any charge-relaxation process that is asymmetric with respect to ɛ. However, the asymmetry associated with ordinary scattering events is typically rather weak, and representable by a power-law dependence of τ(ɛ)∼ɛr with /r/≈1 for, for example, electron scattering by acoustic phonons. Replacing 1/∂ɛ in equation (1) by 1/kB∂T, one immediately recognizes that an enhanced gradient of μH with respect to T similarly can supply a finite Nernst coefficient ν=ATdμH/dT, where A=−(π2/3) kB//e/. As can be seen in Fig. 4, the pronounced ν(T) peak observed slightly below 40 K for Co0.999Ni0.001Sb3 follows this prediction quantitatively, underlining the existence of distinctly different charge mobilities at the two ends of the sample when exposed to a temperature gradient (cf. Figs 1c and 3a). Given that above 40 K μH(T) is only weakly dependent on temperature, one expects ν(T)∝μH(T) (dμH/dT is approximated to first order as μH/T, cf. ref. 9). This is also confirmed in Fig. 4 and at T>40 K, ν(T) scales well with μH(T) (red dashed line).


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 Nernst coefficient of Co0.999Ni0.001Sb3.The green solid line represents ATdμH/dT, the expected contribution to ν(T) from the marked charge mobility change (cf. equation (1)), where the prefactor A=−(π2/3) kB//e/. The quantitative agreement found below 40 K between this calculation and the measured Nernst coefficient (black symbols) lends strong evidence that the enhanced Nernst signal originates from the significant mobility mismatch across the sample. The red dashed line displays the Hall mobility μH(T). ν(T) is expected to approximately scale with μH(T) assuming a weak temperature dependence of the latter, which indeed holds above 40 K (see text for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: The Nernst coefficient of Co0.999Ni0.001Sb3.The green solid line represents ATdμH/dT, the expected contribution to ν(T) from the marked charge mobility change (cf. equation (1)), where the prefactor A=−(π2/3) kB//e/. The quantitative agreement found below 40 K between this calculation and the measured Nernst coefficient (black symbols) lends strong evidence that the enhanced Nernst signal originates from the significant mobility mismatch across the sample. The red dashed line displays the Hall mobility μH(T). ν(T) is expected to approximately scale with μH(T) assuming a weak temperature dependence of the latter, which indeed holds above 40 K (see text for details).
Mentions: Here the energy derivative of the tangent of the Hall angle can be expressed by using either μH or τ because tanθH=eBτ/m*=μHB, where m* denotes the effective mass of the relevant charge carriers. Apparently, ν is sensitive to any charge-relaxation process that is asymmetric with respect to ɛ. However, the asymmetry associated with ordinary scattering events is typically rather weak, and representable by a power-law dependence of τ(ɛ)∼ɛr with /r/≈1 for, for example, electron scattering by acoustic phonons. Replacing 1/∂ɛ in equation (1) by 1/kB∂T, one immediately recognizes that an enhanced gradient of μH with respect to T similarly can supply a finite Nernst coefficient ν=ATdμH/dT, where A=−(π2/3) kB//e/. As can be seen in Fig. 4, the pronounced ν(T) peak observed slightly below 40 K for Co0.999Ni0.001Sb3 follows this prediction quantitatively, underlining the existence of distinctly different charge mobilities at the two ends of the sample when exposed to a temperature gradient (cf. Figs 1c and 3a). Given that above 40 K μH(T) is only weakly dependent on temperature, one expects ν(T)∝μH(T) (dμH/dT is approximated to first order as μH/T, cf. ref. 9). This is also confirmed in Fig. 4 and at T>40 K, ν(T) scales well with μH(T) (red dashed line).

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