Session 1A - Inaugural Session and Presidential Addres

Metavalent bonding: Origins of unusual properties of group IV chalcogenide crystals

A distinct type of metavalent (intermediate to metallic and covalent) bonding (MVB) was recently proposed to explain an unusual combination of anomalous functional properties of group IV chalcogenide crystals, whose electronic mechanisms and origins remain mysterious. Through theoretical analysis of the evolution of bonding along continuous paths in structural and chemical composition space, we demonstrate the emergence of MVB in rocksalt chalcogenides as a consequence of weakly broken symmetry of parent metallic simple-cubic crystals of Group V metalloids. Stronger symmetry-breaking structural and chemical fields, however, transform them discontinuously to covalent and ionic semiconducting states, respectively. MVB involves an electron engaged in bonding and antibonding pairwise interactions alternating along linear chains of atoms, which facilitate electronic delocalization and long-range electron transfer in response to polar fields and cause unusual properties. Understanding ofMVB is central to the design of quantum materials exhibiting thermoelectric, ferroelectric and nontrivial electronic topological properties.