Intersite elastic coupling and invar effect

TL;DR

This paper explains the invar effect, characterized by minimal thermal expansion in certain iron alloys, by considering elastic interactions between different spin states of Fe atoms, providing a new understanding of this phenomenon.

Contribution

It introduces a model incorporating elastic interactions between Fe atoms in different spin states to explain the invar effect, advancing prior explanations based solely on spin state transitions.

Findings

Elastic interactions can suppress thermal expansion over broad temperature ranges

The model accounts for the near-zero thermal expansion characteristic of invar alloys

Provides a theoretical basis for designing materials with minimal thermal expansion

Abstract

The invar phenomenon (very small thermal expansion in some iron alloys or compounds) is usually explained by the thermally-induced transitions between different spin states of Fe, having different atomic volumes. We consider these processes taking into account elastic interaction between Fe atoms in different spin states. Inclusion of these interactions explains why thermal expansion may be close to zero in a broad temperature interval and thus gives rise to the invar effect.