Chemical bonding in chalcogenides: the concept of multi-centre hyperbonding

TL;DR

This paper introduces the concept of multi-centre hyperbonding in chalcogenides, revealing how delocalized electron interactions influence material properties and phase differences, aiding in the design of better chalcogenide materials.

Contribution

It presents a new chemical-bonding framework based on multi-centre hyperbonding, derived from DFT-MD simulations, to explain bonding and properties in chalcogenides.

Findings

Identification of multi-centre hyperbonding interactions

Explanation of property differences between amorphous and crystalline phases

Revealing similar bonding nature in crystalline and amorphous PCMs

Abstract

The precise nature of chemical-bonding interactions in amorphous, and crystalline, chalcogenides is still unclear due to the complexity arising from the delocalization of bonding, and non-bonding, electrons. Although an increasing degree of electron delocalization for elements down a column of the periodic table is widely recognized, its influence on chemical-bonding interactions, and on consequent material properties, of chalcogenides has not previously been comprehensively understood from an atomistic point of view. Here, we provide a chemical-bonding framework for understanding the behaviour of chalcogenides (and, in principle, other lone-pair materials) by studying prototypical Telluride non-volatile-memory, 'phase-change' materials (PCMs), and related chalcogenide compounds, via density-functional-theory, molecular-dynamics (DFT-MD) simulations. Identification of the presence of previously unconsidered multi-centre 'hyperbonding' (lone-pair-antibonding-orbital) interactions elucidates not only the origin of various material properties, and their contrast in magnitude between amorphous and crystalline phases, but also the very similar chemical-bonding nature between crystalline PCMs and one of the bonding subgroups (with the same bond length) found in amorphous PCMs, in marked contrast to existing viewpoints. The structure-property relationship established from this new bonding-interaction perspective will help in designing improved chalcogenide materials for diverse applications, based on a fundamental chemical-bonding point of view.