From phase-change materials to thermoelectrics: The role of metavalent bonding

Abstract Excellent phase-change memory materials and thermoelectrics are often found in chalcogenide compounds, in which they share a unique portfolio of properties. Quantum-chemical calculations indicate that these solids are characterized by the sharing of about one electron and a small number of electron transfers. In addition, atom probe tomography reveals an abnormal bond-breaking behavior. All of these factors indicate an unconventional bonding mechanism that differs from classical covalent, ionic, and metallic bonding, termed metavalent bonding. The adaptation of this bonding mechanism holds great potential for the development of phase-change and thermoelectric materials. For example, non-Zachariasen glasses have been identified for optoelectronic applications, where the crystallization rate can be tuned by changing the degree of electron sharing. Thermoelectric performance can also be significantly improved by forming metavalent bonds. Therefore, metavalent bonding offers a high degree of predictive power in tailoring properties for phase-change and thermoelectric applications. Graphical abstract