Descriptors for thermal expansion in solids

TL;DR

This paper introduces a set of simple, accessible descriptors based on ionic radii and bond coordination that can rapidly predict the thermal expansion properties of solids, aiding material selection.

Contribution

It identifies and combines key ionic and structural descriptors to effectively predict thermal expansion, simplifying the screening process for materials with desired thermal properties.

Findings

Descriptors correlate with room-temperature thermal expansion.

Combining descriptors improves prediction accuracy.

Open space and low coordination lead to lower thermal expansion.

Abstract

Thermal expansion in materials can be accurately modeled with careful anharmonic phonon calculations within density functional theory. However, because of interest in controlling thermal expansion and the time consumed evaluating thermal expansion properties of candidate materials, either theoretically or experimentally, an approach to rapidly identifying materials with desirable thermal expansion properties would be of great utility. When the ionic bonding is important in a material, we show that the fraction of crystal volume occupied by ions, (based upon ionic radii), the mean bond coordination, and the deviation of bond coordination are descriptors that correlate with the room-temperature coefficient of thermal expansion for these materials found in widely accessible databases. Correlation is greatly improved by combining these descriptors in a multi-dimensional fit. This fit reinforces the physical interpretation that open space combined with low mean coordination and a variety of local bond coordinations leads to materials with lower coefficients of thermal expansion, materials with single-valued local coordination and less open space have the highest coefficients of thermal expansion.