Absence of Metastable States in Strained Monatomic Cubic Crystals

TL;DR

This study demonstrates that metastable tetragonal phases in monatomic cubic crystals are generally unstable without substrate stabilization, based on combined tight-binding and first-principles calculations along the Bain path.

Contribution

It provides a comprehensive analysis showing the instability of local minima along the Bain path in monatomic cubic crystals, emphasizing the role of substrates in stabilizing such phases.

Findings

Local minima along the Bain path are unstable without substrate support.

Only at the bcc or fcc points are the minima stable.

Epitaxially grown thin films require substrate stabilization for tetragonal phases.

Abstract

A tetragonal (Bain path) distortion of a metal with an fcc (bcc) ground state will initially cause an increase in energy, but at some point along the Bain path the energy will again decrease until a local minimum is reached. Using a combination of parametrized tight-binding and first-principles LAPW calculations we show that this local minimum is unstable with respect to an elastic distortion, except in the rare case that the minimum is at the bcc (fcc) point on the Bain path. This shows that body-centered tetragonal phases of these materials, which have been seen in epitaxially grown thin films, must be stabilized by the substrate and cannot be free-standing films.