Finite strain Landau theory of high pressure phase transformations

TL;DR

This paper extends Landau theory to describe high-pressure structural phase transformations in materials, incorporating finite strains and nonlinear elastic effects for better understanding of Earth's interior processes.

Contribution

It develops a nonlinear Landau theory framework that accounts for finite strains and nonlinear elasticities in high-pressure phase transformations.

Findings

Effective modeling of phase transformations up to ultrahigh pressures

Inclusion of finite strains improves transition descriptions

Framework applicable to a wide range of materials

Abstract

The properties of materials near structural phase transitions are often successfully described in the framework of Landau theory. While the focus is usually on phase transitions, which are induced by temperature changes approaching a critical temperature T-c, here we will discuss structural phase transformations driven by high hydrostatic pressure, as they are of major importance for understanding processes in the interior of the earth. Since at very high pressures the deformations of a material are generally very large, one needs to apply a fully nonlinear description taking physical as well as geometrical nonlinearities (finite strains) into account. In particular it is necessary to retune conventional Landau theory to describe such phase transitions. In Troster et al (2002 Phys. Rev. Lett. 88 55503) we constructed a Landau-type free energy based on an order parameter part, an order parameter-(finite) strain coupling and a nonlinear elastic term. This model provides an excellent and efficient framework for the systematic study of phase transformations for a wide range of materials up to ultrahigh pressures.