Explaining the Entropy Forming Ability with the atomic size mismatch

TL;DR

This paper investigates the entropy forming ability (EFA) in multi-principal-element materials, revealing that atomic size mismatch, rather than configurational entropy, governs phase stability, aligning with Hume-Rothery rules.

Contribution

It demonstrates that atomic size mismatch correlates inversely with EFA and influences phase stability, challenging the traditional emphasis on configurational entropy.

Findings

EFA correlates inversely with lattice distortion.

Large atomic size differences promote multi-phase formation.

Hume-Rothery rules apply to complex ceramics' phase stability.

Abstract

To quickly screen for single-phased multi-principal-element materials, a so-called entropy forming ability (EFA) parameter is sometimes used as a descriptor. The higher the EFA, the higher is the propensity to form a single-phase structure, which is stabilized against separation up to a certain threshold by the configurational entropy. We have investigated this EFA descriptor with atomic relaxations in special-quasi-random structures and discovered that the EFA correlates inversely with the lattice distortion. Large atomic size differences lead to multi-phase compounds, and little size differences to single-phase compounds. Instead of configurational entropy, we therefore demonstrate the applicability of the Hume-Rothery rules to phase stability of solid solutions even in compositionally complex ceramics.