Unlocking the potential of coinage-based quaternary chalcogenides for thermoelectricity

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2024-03, Vol.12 (1), p.5846-5857
• Main Authors: Gholami, Mahsa, Hajiahmadi, Zahra, Naghavi, S. Shahab
• Format: Article
• Language: English
• Subjects: Anharmonicity; Antimony; Bismuth; Bonding strength; Chalcogenides; Copper; Gallium; Germanium; Gold; Heat conductivity; Heat transfer; Hybridization; Lead; Power factor; Silver; Thermal conductivity; Thermoelectric materials; Tin; Transition metals; Unit cell; Valence band
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d3ta07747k

The pursuit of thermoelectric materials poses a formidable challenge, given that numerous predicted candidates fail in real-world applications. An effective way to enhance the success rate of computer predictions is to focus on key elements shared by workable thermoelectrics. These elements include chalcogens (Q = S and Se), pentagons (III = &z.dbd;As, Sb, and Bi), coinage metals (I = &z.dbd;Cu, Ag, and Au), and post-transition metals (III/IV = &z.dbd;Ga, In, Ge, Sn, Pb). Here, we screen two types of coinage-based quaternary chalcogenides possessing these crucial thermoelectric elements: I-II-IV-Q 4 and I-II 2 -III-Q 4 . We found that the thermoelectric performance of these compounds originates from the unconventional I-Q bonding formed through strong coupling between the coinage d and chalcogen p orbitals. The d-p hybridization forms a filled antibonding state at the top of the valence band that not only weakens the I-Q bonds, which lowers the lattice thermal conductivity, but also generates a flat-and-dispersive and multi-valley degenerate valence band, resulting in a high p-type power factor. So, the higher the share of coinage metals and thus the I-Q bonding within the unit cell, the lower the lattice thermal conductivity is. Such soft I-Q bonds, when accompanied by breakage of local symmetry and corner-sharing tetrahedral units, suppress the lattice thermal conductivity down to the amorphous limit. For instance, Ag 2 PbGeS 4 demonstrates a lattice thermal conductivity of 0.15 W m −1 K −1 because of various anharmonic scattering processes caused by lone-pair-induced off-centering of Pb, weak Ag-Ag interactions, and disrupted corner-sharing networks, the combination that yields a zT exceeding two. Our findings highlight the potential of coinage-based quaternary chalcogenides as practical thermoelectric materials, paving the way for the development of customizable thermoelectrics. The pursuit of thermoelectric materials poses a formidable challenge, given that numerous predicted candidates fail in real-world applications.