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The synthesis and characterization of both single crystals and polycrystalline samples of the novel quaternary Rb0.2Ba0.4Cr5Se8 were performed. The compound crystallizes in a monoclinic crystal system (space group C2/m, cell parameters a = 18.707 Å, b = 3.603 Å, c = 8.964 Å, β = 104.49 °), isostructural to pseudo-hollandite compounds. The presence of a mixed occupancy of both Rb and Ba on the 2a site in the middle of the one-dimensional channel-like structure was confirmed, inducing a higher crystal symmetry compared to the related compound Ba0.5Cr5Se8 (space group P1 ̅). High-temperature powder X-ray diffraction experiments revealed no decomposition up to 973 K, and the thermal expansion coefficient was determined to be 2.6(1).10-5 K-1 at 300 K. Spin-polarized DFT calculations revealed that the density of states of Rb0.2Ba0.4Cr5Se8 is more polarized than that of Ba0.5Cr5Se8, resulting in a higher computed Seebeck coefficient. This was confirmed experimentally with a maximum value of 400 µV.K-1 at 620 K, higher than that of other pseudo-hollandite thermoelectric compounds which exhibit values below 300 µV.K-1 at comparable temperatures. Resistivity measurements showed a degenerate semiconducting behavior below 550 K, ρ reaching 100 mΩ.cm at that temperature, leading to an improved maximum power factor of 0.21 mW.m-1.K-2 for Rb0.2Ba0.4Cr5Se8 compared to 0.12 mW.m-1.K-2 for Ba0.5Cr5Se8. The thermal conductivity of the former exhibits very low values around 0.8 W.m-1.K-1 in the 300 – 900 K temperature range, resulting in a thermoelectric figure of merit of 0.22 at 873 K. A decorrelation of the electrical transport properties is observed in this double-inserted Rb0.2Ba0.4Cr5Se8 pseudo-hollandite, leading to improved properties and making this compound a good example of beneficial synergistic effects for higher performance thermoelectric materials.

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• In Copyright
  This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Inorganic Chemistry, copyright © 2024 American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.4c01867

Keyword: thermoelectric

Date published: 2024-09-09

Publisher: American Chemical Society (ACS)

Journal:

• Inorganic Chemistry (ISSN: 1520510X) vol. 63 issue. 36 p. 16655-16666

Funding:

• JST-Mirai Program JPMJMI19A1
• Agence Nationale de la Recherche ANR-18-CE05-0037
• Japan Society for the Promotion of Science 19H05819
• Japan Society for the Promotion of Science PE21708

Manuscript type: Author's original (Submitted manuscript)

MDR DOI: https://doi.org/10.48505/nims.4802

First published URL: https://doi.org/10.1021/acs.inorgchem.4c01867

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Updated at: 2024-10-07 14:41:57 +0900

Published on MDR: 2024-10-07 14:41:58 +0900