Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

• Published in: Advanced functional materials Vol. 30; no. 8
• Main Authors: Yu, Yuan, Cagnoni, Matteo, Cojocaru‐Mirédin, Oana, Wuttig, Matthias
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.02.2020
• Subjects: anharmonicity; Anisotropy; band engineering; chalcogenide; Chalcogenides; Chemical bonds; Converters; Corporate governance; Electrical resistivity; Heat conductivity; Heat transfer; Materials science; metavalent bonding; Optimization; Organic chemistry; Parameters; Playgrounds; Seebeck effect; Subgroups; Thermal conductivity; thermoelectric; Thermoelectric materials
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201904862

Thermoelectric materials have attracted significant research interest in recent decades due to their promising application potential in interconverting heat and electricity. Unfortunately, the strong coupling between the material parameters that determine thermoelectric efficiency, i.e., the Seebeck coefficient, electrical conductivity, and thermal conductivity, complicates the optimization of thermoelectric energy converters. Main‐group chalcogenides provide a rich playground to alleviate the interdependence of these parameters. Interestingly, only a subgroup of octahedrally coordinated chalcogenides possesses good thermoelectric properties. This subgroup is also characterized by other outstanding characteristics suggestive of an exceptional bonding mechanism, which has been coined metavalent bonding. This conclusion is further supported by a map that separates different bonding mechanisms. In this map, all octahedrally coordinated chalcogenides with good performance as thermoelectrics are located in a well‐defined region, implying that the map can be utilized to identify novel thermoelectrics. To unravel the correlation between chemical bonding mechanism and good thermoelectric properties, the consequences of this unusual bonding mechanism on the band structure are analyzed. It is shown that features such as band degeneracy and band anisotropy are typical for this bonding mechanism, as is the low lattice thermal conductivity. This fundamental understanding, in turn, guides the rational materials design for improved thermoelectric performance by tailoring the chemical bonding mechanism. The outstanding thermoelectric performance of pristine half‐filled p‐bonded chalcogenides with octahedral arrangements can be understood from a chemical bonding perspective, where different bonding mechanisms can be separated in a map depicting the electrons transferred and/or shared between adjacent atoms. Metavalent bonding is responsible for the large band degeneracy, the band anisotropy, and the low lattice thermal conductivity, giving rise to a promising thermoelectric performance.