Interplay between Fe(II) and Fe(III) and Its Impact on Thermoelectric Properties of Iron-Substituted Colusites Cu26−xFexV2Sn6S32

• Published in: Compounds Vol. 3; no. 2; pp. 348 - 364
• Main Authors: Polevik, Alexey O., Sobolev, Alexey V., Glazkova, Iana S., Presniakov, Igor A., Verchenko, Valeriy Yu, Link, Joosep, Stern, Raivo, Shevelkov, Andrei V.
• Format: Journal Article
• Language: English
• Published: MDPI AG 01-06-2023
• Subjects: colusites; crystal structure; magnetic susceptibility; Mössbauer spectroscopy; sulfides; thermoelectric properties
• ISSN: 2673-6918; 2673-6918
• DOI: 10.3390/compounds3020027

Following the trend of finding better thermoelectric materials among synthetic analogs of copper–chalcogenide minerals, we have synthesized iron-bearing colusites of a general formula Cu26−xFexV2Sn6S32. They crystallize in the cubic space group P-43n with the unit cell parameter increasing linearly with the iron content. At a low iron concentration, the crystal structure features disorder manifested by an anti-site effect and a shift of a part of the tin atoms from their ideal positions, which is absent for higher iron contents. The magnetization and 57Fe/119Sn Mössbauer studies showed that, for x = 1, iron is present as Fe3+, whereas for x > 1, Fe2+ and Fe3+ coexist. Additionally, weak antiferromagnetic interactions between iron atoms and fast on the 57Fe Mössbauer time scale (107–109 s−1) electron transfer between adjacent Fe2+ and Fe3+ centers were revealed. Thermoelectric studies showed that iron-bearing colusites are p-type semiconductors with low thermal conductivity stemming from their complex crystal structure and structural disorder. The highest ZT of 0.78 at 700 K was found for the x = 1 iron content, where iron is present as Fe3+ only.