A model solid-state structural transformation: Tetragonal to Orthorhombic

TL;DR

This paper investigates a two-dimensional particle system undergoing a transition from a square to a rhombic lattice, providing insights into the thermodynamics and phase behavior of tetragonal to orthorhombic transformations.

Contribution

It introduces a simplified model capturing the tetragonal to orthorhombic transition, bridging microscopic and continuum descriptions, and explores its thermodynamic properties through multiple methods.

Findings

Phase diagram characterized as a function of density and interaction strengths.

Identification of conditions favoring the structural transition.

Validation of the model as a test bed for studying structural dynamics.

Abstract

We study equilibrium properties of a system of particles in two dimensions, interacting with pair and three body potentials, which undergoes a structural transition from a square to a rhombic lattice and thus constitutes a simple model for a generic tetragonal to orthorhombic transition. We aim at an intermediate level of description lying in-between that of coarse grained elastic strain hamiltonians and microscopic ab-initio approaches. Macroscopic thermodynamic properties and phase diagram at zero and finite temperatures as a function of the density and the relative strengths of the pair and three body energies are obtained using lattice sums, an approximate `cell-model' theory and molecular dynamics simulations in the NVT ensemble. We propose that this model solid can be used as a test bed for studies of statics and dynamics of structural transitions.