Exploring Chemical Bonding in Phase‐Change Materials with Orbital‐Based Indicators

Abstract

The atomic-scale structures of chalcogenide phase-change materials (PCMs) are directly relevant for macroscopic properties and practical applications. In PCMs and throughout materials science, quantum-mechanically based atomistic simulations and chemical-bonding analyses are increasingly helping to understand structures and properties of solids. Here, new insights into PCMs are highlighted that have recently been obtained from orbital-based bonding indicators-in particular, from crystal orbital Hamilton population (COHP) analysis. Applications of these methods in other areas of solid-state and materials chemistry are also discussed, from classical to emerging topics, which may have useful lessons for PCM research in store. It is hoped that this overview will inspire research in the field and enable new chemical insight into structures and properties of PCMs.

Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

“…Figure 6 shows the COHP analyses of Ge-Sb-Te phase change materials which can also be good thermoelectrics. [59,61] By assuming a fully occupied sublattice, i.e., Ge 2 Sb 2 Te 4 , the COHP analysis shows strong antibonding interactions at the Fermi level, as indicated by the red arrow. This is not surprising, since in Ge 2 Sb 2 Te 4 an average of 3.25 p-electrons occupies the lattice sites, leading to a population of antibonding states.…”

“…Reproduced with permission. [61] Copyright 2019, WILEY-VCH. in energy of carrier pockets not related by symmetry, hence enhancing the overall degeneracy.…”

LOBSTER: Local Orbital Projections, Atomic Charges, and Chemical Bonding Analysis from Projector-Augmented-Wave-Based DFT

“…Recent development has also added two major features, namely atomic charges and related populations directly from the wavefunction as well as the -dependent COHP. The former is useful for examining ionic bonding in suchlike (or polar) compounds, for example simple salts, Zintl phases, intermetallics, thermoelectrics, or even phase-change materials, [22][23] [23], [37]- [39] whereas the latter serves useful for detailed band-wise and -point-wise chemical bonding analysis.…”

Phase Change Materials and Superlattices for Non‐Volatile Memories

“…Philipp Konze et al focused on the chemical‐bonding properties of PCMs. The bonding analyses reviewed in this article were primarily made by the crystal orbital Hamilton population (COHP) method.…”