Intermediate states at structural phase transition: Model with a one-component order parameter coupled to strains

TL;DR

This paper models a two-dimensional structural phase transition with a single order parameter coupled to strains, revealing intermediate states where ordered and disordered regions coexist, influenced by elastic coupling near tricriticality.

Contribution

It introduces a Ginzburg-Landau model incorporating elastic coupling to explain intermediate states in structural phase transitions.

Findings

Intermediate states coexistence on mesoscopic scales.

Width of the intermediate state window increases with dilational coupling.

Phase diagrams align with simulation results.

Abstract

We study a Ginzburg-Landau model of structural phase transition in two dimensions, in which a single order parameter is coupled to the tetragonal and dilational strains. Such elastic coupling terms in the free energy much affect the phase transition behavior particularly near the tricriticality. A characteristic feature is appearance of intermediate states, where the ordered and disordered regions coexist on mesoscopic scales in nearly steady states in a temperature window. The window width increases with increasing the strength of the dilational coupling. It arises from freezing of phase ordering in inhomogeneous strains. No impurity mechanism is involved. We present a simple theory of the intermediate states to produce phase diagrams consistent with simulation results.