Structure Evolution and Bonding Inhomogeneity toward High Thermoelectric Performance in Cu2CoSnS4- xSex Materials

Taras Parashchuk; Oleksandr Cherniushok; Oleksandr Smitiukh; Oleg Marchuk; Krzysztof T Wojciechowski

doi:10.1021/acs.chemmater.3c00586

Structure Evolution and Bonding Inhomogeneity toward High Thermoelectric Performance in Cu₂CoSnS_{4- x}Se_x Materials

Chem Mater. 2023 Jun 7;35(12):4772-4785. doi: 10.1021/acs.chemmater.3c00586. eCollection 2023 Jun 27.

Authors

Taras Parashchuk¹, Oleksandr Cherniushok¹, Oleksandr Smitiukh², Oleg Marchuk², Krzysztof T Wojciechowski¹

Affiliations

¹ Thermoelectric Research Laboratory, Department of Inorganic Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza Ave. 30, 30-059 Krakow, Poland.
² Department of Chemistry and Technology, Volyn National University, Voli Ave 13, Lutsk 43025, Ukraine.

Abstract

Lightweight diamond-like structure (DLS) materials are excellent candidates for thermoelectric (TE) applications due to their low costs, eco-friendly nature, and property stability. The main obstacles restricting the energy-conversion performance by the lightweight DLS materials are high lattice thermal conductivity and relatively low carrier mobility. By investigating the anion substitution effect on the structural, microstructural, electronic, and thermal properties of Cu₂CoSnS_4-xSe_x, we show that the simultaneous enhancement of the crystal symmetry and bonding inhomogeneity engineering are effective approaches to enhance the TE performance in lightweight DLS materials. Particularly, the increase of x in Cu₂CoSnS_4-xSe_x makes the DLS structure with the ideal tetrahedral bond angles of 109.5° favorable, leading to better crystal symmetry and higher carrier mobility in samples with higher selenium content. In turn, the phonon transport in the investigated DLS materials is strongly disturbed due to the bonding inhomogeneity between anions and three sorts of cations inducing large lattice anharmonicity. The increase of Se content in Cu₂CoSnS_4-xSe_x only intensified this effect resulting in a lower lattice component of the thermal conductivity (κ_L) for Se-rich samples. As a result of the enhanced power factor S²ρ^-1 and the low κ_L, the dimensionless thermoelectric figure of merit ZT achieves a high value of 0.75 for Cu₂CoSnSe₄ DLS material. This work demonstrates that crystal symmetry and bonding inhomogeneity play an important role in the transport properties of DLS materials and provide a path for the development of new perspective materials for TE energy conversion.