Entropy-Induced Multivalley Band Structures Improve Thermoelectric Performance in p-Cu7P(SxSe1- x)6 Argyrodites

Oleksandr Cherniushok; Taras Parashchuk; Janusz Tobola; Son D N Luu; Artem Pogodin; Oleksandr Kokhan; Ihor Studenyak; Igor Barchiy; Michal Piasecki; Krzysztof T Wojciechowski

doi:10.1021/acsami.1c11193

Entropy-Induced Multivalley Band Structures Improve Thermoelectric Performance in p-Cu₇P(S_xSe_{1- x})₆ Argyrodites

ACS Appl Mater Interfaces. 2021 Aug 25;13(33):39606-39620. doi: 10.1021/acsami.1c11193. Epub 2021 Aug 13.

Authors

Oleksandr Cherniushok^{1

2}, Taras Parashchuk^{1

2}, Janusz Tobola³, Son D N Luu^{2

4}, Artem Pogodin⁵, Oleksandr Kokhan⁵, Ihor Studenyak⁵, Igor Barchiy⁵, Michal Piasecki⁶, Krzysztof T Wojciechowski^{1

2}

Affiliations

¹ Thermoelectric Research Laboratory, Department of Inorganic Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, 30 Mickiewicza Avenue, 30-059 Krakow, Poland.
² Lukasiewicz Research Network, Krakow Institute of Technology, Zakopianska 73, 30-418 Krakow, Poland.
³ Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, 30-059 Krakow, Poland.
⁴ Institute of Research and Development, Duy Tan University, Da Nang 550000, Viet Nam.
⁵ Uzhhorod National University, Pidhirna 46, 88000 Uzhhorod, Ukraine.
⁶ Theoretical Physics Department, Jan Długosz University, Armii Krajowej 13/15, 42200 Częstochowa, Poland.

PMID: 34387484
DOI: 10.1021/acsami.1c11193

Abstract

Searching for novel low-cost and eco-friendly materials for energy conversion is a good way to provide widespread utilization of thermoelectric technologies. Herein, we report the thermal behavior, phase equilibria data, and thermoelectric properties for the promising argyrodite-based Cu₇P(S_xSe_1-x)₆ thermoelectrics. Alloying of Cu₇PSe₆ with Cu₇PS₆ provides a continuous solid solution over the whole compositional range, as shown in the proposed phase diagram for the Cu₇PS₆-Cu₇PSe₆ system. As a member of liquid-like materials, the investigated Cu₇P(S_xSe_1-x)₆ solid solutions possess a dramatically low lattice thermal conductivity, as low as ∼0.2-0.3 W m^-1 K^-1, over the entire temperature range. Engineering the configurational entropy of the material by introducing more elements stabilizes the thermoelectrically beneficial high-symmetry γ-phase and promotes the multivalley electronic structure of the valence band. As a result, a remarkable improvement of the Seebeck coefficient and a reduction of electrical resistivity were observed for the investigated alloys. The combined effect of the extremely low lattice thermal conductivity and enhanced power factor leads to the significant enhancement of the thermoelectric figure of merit ZT up to ∼0.75 at 673 K for the Cu₇P(S_xSe_1-x)₆ (x = 0.5) sample with the highest configurational entropy, which is around twice higher compared with the pure selenide and almost four times higher than sulfide. This work not only demonstrates the large potential of Cu₇P(S_xSe_1-x)₆ materials for energy conversion but also promotes sulfide argyrodites as earth-abundant and environmentally friendly materials for energy conversion.

Keywords: Cu-based argyrodites; electronic structure; entropy engineering; liquid-like materials; multivalley band structure; solid solution; thermoelectric properties.