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Hejtmánek, J.; Jirák, Z.; Šebek, J.

doi:10.1103/physrevb.92.125106

Cited by 17 publications

(10 citation statements)

References 35 publications

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“…In this paper, we will consider an alternative model for the Seebeck coefficient, which is the so-called Kelvin formula for the thermopower [32]. The Kelvin formula recently gained interest in theoretical condensed matter physics and has been shown to yield a good approximation of the Seebeck coefficient for many materials (including semiconductors, metals and high temperature superconductors) at reasonably high temperatures [32][33][34][35][36][37][38][39][40][41][42]. The Kelvin formula relates the Seebeck coefficient to the derivative of the entropy density with respect to the carrier density and therefore involves only equilibrium properties of the electron-hole plasma, where degeneration effects are easily included.…”

Section: Introductionmentioning

confidence: 99%

Generalized Scharfetter–Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient

Kantner

2020

Journal of Computational Physics

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Many challenges faced in today's semiconductor devices are related to self-heating phenomena. The optimization of device designs can be assisted by numerical simulations using the non-isothermal drift-diffusion system, where the magnitude of the thermoelectric cross effects is controlled by the Seebeck coefficient. We show that the model equations take a remarkably simple form when assuming the so-called Kelvin formula for the Seebeck coefficient. The corresponding heat generation rate involves exactly the three classically known self-heating effects, namely Joule, recombination and Thomson-Peltier heating, without any further (transient) contributions. Moreover, the thermal driving force in the electrical current density expressions can be entirely absorbed in the diffusion coefficient via a generalized Einstein relation. The efficient numerical simulation relies on an accurate and robust discretization technique for the fluxes (finite volume Scharfetter-Gummel method), which allows to cope with the typically stiff solutions of the semiconductor device equations. We derive two non-isothermal generalizations of the Scharfetter-Gummel scheme for degenerate semiconductors (Fermi-Dirac statistics) obeying the Kelvin formula. The approaches differ in the treatment of degeneration effects: The first is based on an approximation of the discrete generalized Einstein relation implying a specifically modified thermal voltage, whereas the second scheme follows the conventionally used approach employing a modified electric field. We present a detailed analysis and comparison of both schemes, indicating a superior performance of the modified thermal voltage scheme.

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Section: Introductionmentioning

confidence: 99%

Generalized Scharfetter–Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient

Kantner

2020

Journal of Computational Physics

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“…1) [7]: The CdI 2 -type CoO 2 layer responsible for the charge transport and the rocksalt-type Ca 2 CoO 3 layer which behaves as the charge reservoir to supply holes into the CoO 2 layer [8][9][10][11]. The anomalous charge transport of this compound is clearly seen in the non-monotonic temperature variations of the electrical resistivity and the Seebeck coefficient [7,[12][13][14][15], but an underlying origin for these behaviors remains unclear. For instance, below T ∼ 60 K, the resistivity increases with decreasing temperature like an insulator while the Seebeck coefficient shows a metallic behavior, which has been discussed in terms of the variable range hopping [16], quantum criticality [17], and pseudogap opening [18] associated with a spin-density-wave (SDW) formation [19].…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric transport in the layered Ca3Co4–xRhxO9 single crystals

Ikeda

Saito

Okazaki

2016

Journal of Applied Physics

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We have examined an isovalent Rh substitution effect on the transport properties of the thermoelectric oxide Ca 3 Co 4 O 9 using single-crystalline form. With increasing Rh content x, both the electrical resistivity and the Seebeck coefficient change systematically up to x = 0.6 for Ca 3 Co 4−x Rh x O 9 samples. In the Fermi-liquid regime where the resistivity behaves as ρ = ρ 0 + AT 2 around 120 K, the A value decreases with increasing Rh content, indicating that the correlation effect is weakened by Rh 4d electrons with extended orbitals. We find that, in contrast to such a weak correlation effect observed in the resistivity of Rh-substituted samples, the low-temperature Seebeck coefficient is increased with increasing Rh content, which is explained with a possible enhancement of a pseudogap associated with the short-range order of spin density wave. In high-temperature range above room temperature, we show that the resistivity is largely suppressed by Rh substitution while the Seebeck coefficient becomes almost temperature-independent, leading to a significant improvement of the power factor in Rh-substituted samples. This result is also discussed in terms of the differences in the orbital size and the associated spin state between Co 3d and Rh 4d electrons.

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“…At this temperature, a small anomaly has been observed in several quantities such as the resistivity, magnetic susceptibility, heat capacity, and lattice constants [18,22,39]. On the other hand, the magnitude of the resistive anomaly may be sample-dependent [40] and is not resolved in the present samples. Although the present measurements are limited below 600 K, the increase of thermopower may continue up to 1000 K according to hightemperature transport experiments in this compound [41].…”

Section: Methodsmentioning

confidence: 58%

Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]

Sakabayashi,

Okazaki

2021

Preprint

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The layered cobaltite [Ca 2 CoO 3 ] 0.62 [CoO 2 ], often expressed as the approximate formula Ca 3 Co 4 O 9 , is a promising candidate for efficient oxide thermoelectrics but an origin of its unusual thermoelectric transport is still in debate. Here we investigate in-plane anisotropy of the transport properties in a broad temperature range to examine the detailed conduction mechanism. The in-plane anisotropy between a and b axes is clearly observed both in the resistivity and the thermopower, which is qualitatively understood with a simple band structure of the triangular lattice of Co ions derived from the angle-resolved photoemission spectroscopy experiments. On the other hand, at high temperatures, the anisotropy becomes smaller and the resistivity shows a temperature-independent behavior, both of which indicate a hopping conduction of localized carriers. Thus the present observations reveal a crossover from low-temperature itinerant to high-temperature localized states, signifying both characters for the enhanced thermopower.

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Spin-entropy contribution to thermopower in the[Ca2CoO3–t]0.62

Cited by 17 publications

References 35 publications

Generalized Scharfetter–Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient

Generalized Scharfetter–Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient

Thermoelectric transport in the layered Ca3Co4–xRhxO9 single crystals

Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]

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