Renormalized bands and low-temperature colossal thermopower induced by Ir doping in Ca3Co4O9 system

Huang, Yang; Zhao, Bangchuan; Lin, Shuai; Song, Wenhai; Sun, Yan

doi:10.1063/1.4820464

Cited by 7 publications

(4 citation statements)

References 24 publications

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“…Using the classical relation R H ¼ 1/ne, these values correspond to a charge carrier concentration n of 5.7 Â 10 20 (0.047 per formula unit) and 3.9 Â 10 20 cm À3 (0.032 per formula unit), respectively. These values are in agreement with carrier concentrations for CCO derived from Hall effect measurements reported by others, [13][14][15][16][17][18][19][20][21]39 but in disagreement with estimates for the charge carrier concentration made from other techniques, as explained in the introduction. In general, the transport properties of CCO are highly anisotropic caused by its layered crystal structure, with relatively high conductivity within the COL (along the ab-direction) and low conductivity across (along c).…”

Section: Resultssupporting

confidence: 90%

Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

Schrade

Norby

Finstad

2015

Journal of Applied Physics

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The Hall coefficient R H and electrical conductivity of misfit calcium cobalt oxide (Ca 2 CoO 3Àd) q (CoO 2) (CCO) were measured at room temperature for different oxygen vacancy concentrations d. Based on these and numerous previous results, it is shown that the charge carrier concentrations n obtained by the classical formula R H ¼ 1/ne are between 3 and 6 Â 10 20 cm À3 and thereby much lower than those derived by other experimental techniques and fail to explain the observed electric properties of CCO. We show that the experimental results are well described using an earlier proposed t-J-model for strongly correlated electrons on a triangular lattice. The hopping parameter t for CCO was found to be % À20 K and the charge carrier concentration of fully oxidized CCO to be 5.7 Â 10 21 cm À3 (0.41 hole type carriers per formula unit), in agreement with other experimental techniques. V

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Section: Resultssupporting

confidence: 90%

Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

Schrade

Norby

Finstad

2015

Journal of Applied Physics

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“…33 However, for our particular system, previous studies have shown that relative changes of p, such as the increase found by us, are qualitatively accurate, as long as data are compared at a constant temperature. [34][35][36][37] We find that the hole carrier density increases by about 20% in the presence of Co 3 O 4 . The larger charge density explains the drop in resistivity both qualitatively and quantitatively.…”

Section: Materials and Experimental Methodsmentioning

confidence: 67%

Thermoelectric properties of [Ca2CoO3−δ][CoO2]1,62 as a function of Co/Ca defects and Co3O4 inclusions

Büttner

Populoh

Xie

et al. 2017

Journal of Applied Physics

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The misfit-layered cobalt oxide [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 is a promising material for hightemperature thermoelectric heat recovery. Here, we show that discrepancies in the numerously reported thermoelectric performances can result from Co 3 O 4 impurities or a change of the defects, i.e., the relative Co content in the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase. We observe that increasing the relative Co content in the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase leads to a larger figure of merit ZT. We attribute this increase of ZT to additional p-type charge carriers introduced by Ca vacancies and the resulting reduction of the electrical resistivity. For Co/Ca ratios above the miscibility limit, the increase in thermal conductivity due to the formation of Co 3 O 4 impurities leads to a reduction of ZT when the volume fraction of the Co 3 O 4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase.

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“…Turning to the Seebeck coefficients, it was found they could be significantly enhanced by substituting Fe 3+ , Mn 4+ or Ir 4+ for Co 3+ in the [CoO 2 ] layers [36,41,58]. Wang et al [36,41] examined the variation in effective mass (m * ) when 2.5 at.% Fe 3+ and Mn 4+ were substituted into calcium cobaltite, and fitted relevant specific heat capacity data using equation ( 5) [59]:…”

Section: Elemental Dopingmentioning

confidence: 99%

“…In particular, the power factor for the 2.5 at.% Fe 3+ substituted material (0.7 mWm −1 K −2 at 1000 K) is nearly triple that for undoped calcium cobaltite. Huang et al [58] proposed that Ir 4+ substitution for Co 3+ enhances the thermopower because Ir doping helps to extend the electronic band in the vicinity of the Fermi level; the band structure is renormalized by enhanced carrier localization. Consequently, the maximum valence band is decreased whilst the band gap is increased, leading to enhanced Seebeck coefficients according to equation ( 6) [65]:…”

Section: Elemental Dopingmentioning

confidence: 99%

Calcium cobaltite, a promising oxide for energy harvesting: effective strategies toward enhanced thermoelectric performance

Freer

2022

J. Phys. Energy

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Thermoelectric (TE) materials are able to generate power from waste heat and thereby provide an alternative source of sustainable energy. Calcium cobaltite is a promising p-type thermoelectric oxide because of its intrinsically low thermal conductivity arising from the misfit layered structure. Its structural framework contains two sublayers with different incommensurate periodicities, offering different sites for substituting elements; the plate-like grain structure contributes to texture development, thereby providing opportunities to modulate the thermoelectric response. In this topical review, we briefly introduce the misfit crystal structure of calcium cobaltite and summarize three efficient strategies to enhance the thermoelectric performance, namely (i) elemental doping, (ii) optimization of fabrication route, and (iii) composite design. For each strategy, examples are presented and performance enhancing mechanisms are discussed. The roles of dopants, processing routes and phase composition are clearly identified to provide insights into processing-structure-property relationship for calcium cobaltite based materials. We outline some of the challenges that still need to be addressed and hope that the proposed strategies can be exploited in other thermoelectric systems.

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Renormalized bands and low-temperature colossal thermopower induced by Ir doping in Ca3Co4O9 system

Cited by 7 publications

References 24 publications

Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

Thermoelectric properties of [Ca2CoO3−δ][CoO2]1,62 as a function of Co/Ca defects and Co3O4 inclusions

Calcium cobaltite, a promising oxide for energy harvesting: effective strategies toward enhanced thermoelectric performance

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