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Open AccessArticle

Thermoelectric Properties of Ca3Co2−xMnxO6 (x = 0.05, 0.2, 0.5, 0.75, and 1)

1
Department of Materials Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
2
Department of Chemistry, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, Norway
*
Author to whom correspondence should be addressed.
Materials 2019, 12(3), 497; https://doi.org/10.3390/ma12030497
Received: 21 January 2019 / Revised: 1 February 2019 / Accepted: 2 February 2019 / Published: 6 February 2019
(This article belongs to the Section Energy Materials)
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Abstract

High-temperature instability of the Ca3Co4−yO9+δ and CaMnO3−δ direct p-n junction causing the formation of Ca3Co2−xMnxO6 has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca3Co2−xMnxO6 with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca3CoMnO6 (x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S·cm−1 at 900 °C for x = 0.05. The material Ca3Co1.8Mn0.2O6 (x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca3Co2−xMnxO6 layers between Ca3Co4−yO9+δ and CaMnO3−δ open for new geometries and designs of oxide-based thermoelectric generators. View Full-Text
Keywords: Ca3Co2−xMnxO6; thermoelectric properties; thermal conductivity; electrical conductivity; Seebeck coefficient Ca3Co2−xMnxO6; thermoelectric properties; thermal conductivity; electrical conductivity; Seebeck coefficient
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Kanas, N.; Singh, S.P.; Rotan, M.; Desissa, T.D.; Grande, T.; Wiik, K.; Norby, T.; Einarsrud, M.-A. Thermoelectric Properties of Ca3Co2−xMnxO6 (x = 0.05, 0.2, 0.5, 0.75, and 1). Materials 2019, 12, 497.

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