Thermoelectric transport in the layered Ca3Co4–xRhxO9 single crystals

We have examined an isovalent Rh substitution effect on the transport properties of the thermoelectric oxide Ca3Co4O9 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 Ca3Co4–xRhxO9 samples...

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Bibliographic Details
Published in:Journal of applied physics 2016-06, Vol.119 (22)
Main Authors: Ikeda Yusuke, Saito Kengo, Okazaki Ryuji
Format: Article
Language:English
Subjects:
Applied physics
Electrical resistivity
Electrons
Power factor
Seebeck effect
Short range order
Single crystals
Spin density waves
Substitutes
Thermoelectricity
Transport properties
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Summary:We have examined an isovalent Rh substitution effect on the transport properties of the thermoelectric oxide Ca3Co4O9 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 Ca3Co4–xRhxO9 samples. In the Fermi-liquid regime where the resistivity behaves as ρ=ρ0+AT2 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.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4953359