Origin of coexisting large Seebeck coefficient and metallic conductivity in the electron doped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>SrTiO</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>KTaO</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

Usui, Hidetomo; Shibata, Shotaro; Kuroki, Kazuhiko

doi:10.1103/physrevb.81.205121

Cited by 41 publications

(53 citation statements)

References 32 publications

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“…(34) onward that all U n tensors equal the identity, which amounts to the usual isotropic relaxation-time approximation for each band n. More technically, we could have retained the form of τ n given in Eq. (C2) and all our major conclusions would have carried over essentially unchanged, except for formal but relatively straightforward generalizations, such as replacing Eq.…”

Section: Appendix C: Anisotropic Tensor Forms Of Relaxation Timesmentioning

confidence: 99%

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Theory of band warping and its effects on thermoelectronic transport properties

et al. 2014

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Optical and transport properties of materials depend heavily upon features of electronic band structures in proximity of energy extrema in the Brillouin zone (BZ). Such features are generally described in terms of multi-dimensional quadratic expansions and corresponding definitions of effective masses. Multi-dimensional quadratic expansions, however, are permissible only under strict conditions that are typically violated when energy bands become degenerate at extrema in the BZ. Even for energy bands that are non-degenerate at critical points in the BZ there are instances in which multi-dimensional quadratic expansions cannot be correctly performed. Suggestive terms such as "band warping", "fluted energy surfaces", or "corrugated energy surfaces" have been used to refer to such situations and ad hoc methods have been developed to treat them. While numerical calculations may reflect such features, a complete theory of band warping has not hitherto been developed. We define band warping as referring to band structures that do not admit second-order differentiability at critical points in k-space and we develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass. Our theory also accounts for effects of band non-parabolicity and anisotropy, which hitherto have not been precisely distinguished from, if not utterly confused with, band warping. Based on our theory, we develop precise procedures to evaluate band warping quantitatively. As a benchmark demonstration, we analyze the warping features of valence bands in silicon using first-principles calculations and we compare those with previous semi-empirical models. As an application of major significance to thermoelectricity, we use our theory and angular effective masses to generalize derivations of tensorial transport coefficients for cases of either single or multiple electronic bands, with either quadratically expansible or warped energy surfaces. From that theory we discover the formal existence at critical points of transport-equivalent ellipsoidal bands that yield identical results from the standpoint of any transport property. Additionally, we illustrate with some basic multi-band models the drastic effects that band warping and anisotropy can induce on thermoelectric properties such as electronic conductivity and thermopower tensors.

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Section: Appendix C: Anisotropic Tensor Forms Of Relaxation Timesmentioning

confidence: 99%

“…Physical effects of that kind have been recently observed by various authors. 31,32,[34][35][36] In Sec. VIII we summarize our conclusions regarding how band warping, band non-parabolicity, anisotropy, multi-valley and multi-band structures can affect and possibly optimize electronic transport for thermoelectricity.…”

Section: 32mentioning

confidence: 99%

Theory of band warping and its effects on thermoelectronic transport properties

et al. 2014

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“…Moreover, m * plays different roles in σ and S. For thermoelectric performance it is important to have both high S and high σ, which as discussed previously 59 have opposite dependences on both carrier concentration and effective mass. This conundrum can be resolved by certain complex band structures that exploit the different transport integrals that enter σ and S. [60][61][62][63][64][65][66] STO has a particular band shape arising from the degeneracy of the t 2g levels in an octahedral crystal field that gives effectively lower dimensional behaviour in transport even though the material is cubic, analogous to the case of PbTe. 65 The sharp onset of the DOS at the CBM reflects the low-dimensional nature of the electronic structure.…”

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confidence: 99%

Thermoelectric properties of n-type SrTiO3

Sun

Singh

2016

APL Materials

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We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

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“…Such an enhancement has been related to the narrowness of the d bands and the abrupt increase of the resistivity near the Fermi level. A similar argument has been, recently, invoked to account for the high Seebeck coefficients measured in some oxides [38][39][40] such as cobaltates, rhodates and perovskites (SrTi0 3 , KTa0 3 and BaTi0 3 ) when suitably doped with electrons and holes. In these cases, doping introduces a narrow additional band that is considered to be responsible for the high |S| values.…”

Section: Resultsmentioning

confidence: 99%

Electronic structure of copper nitrides as a function of nitrogen content

et al. 2013

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The nitrogen content dependence of the electronic properties for copper nitride thin films with an atomic percentage of nitrogen ranging from 26 ± 2 to 33 ± 2 have been studied by means of optical (spectroscopic ellipsometry), thermoelectric (Seebeck), and electrical resistivity measurements. The optical spectra are consistent with direct optical transitions corresponding to the stoichiometric semiconductor Cu 3 N plus a free-carrier contribution, essentially independent of temperature, which can be tuned in accordance with the N-excess. Deviation of the N content from stoichiometry drives to significant decreases from -5 to -50 uV/K in the Seebeck coefficient and to large enhancements, from 10~3 up to 10 O cm, in the electrical resistivity. Band structure and density of states calculations have been carried out on the basis of the density functional theory to account for the experimental results.

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Origin of coexisting large Seebeck coefficient and metallic conductivity in the electron dopedSrTiO3andKTaO3

Cited by 41 publications

References 32 publications

Theory of band warping and its effects on thermoelectronic transport properties

Theory of band warping and its effects on thermoelectronic transport properties

Thermoelectric properties of n-type SrTiO3

Electronic structure of copper nitrides as a function of nitrogen content

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