Pressure-induced structural phase transitions of zirconium: An ab initio study based on statistical ensemble theory

TL;DR

This study uses ab initio ensemble theory to accurately predict pressure-induced phase transitions in zirconium, aligning well with experimental data and clarifying the nature of phase stability at room temperature.

Contribution

It introduces a novel ensemble-theoretic method with ab initio precision to determine phase transitions and provides the first theoretical agreement with multiple experimental results for zirconium.

Findings

Transition pressures of 6.93 GPa and 24.83 GPa for alpha to omega and omega to beta phases.

Parameter-free equation of state matches experimental data within 1.5%.

Supports the non-existence of anharmonicity-driven isostructural transition in beta-phase.

Abstract

The structural phase behaviors of pure zirconium metal under compressions up to $160$ GPa at room temperature are investigated from the perspective of ensemble theory where the partition function is solved by our recently proposed method with \emph{ab initio} precision. The derived Gibbs free energy is employed as the very criterion to determine phase transitions and the calculated transition pressures of the $\alpha\rightarrow\omega\rightarrow\beta$ are $6.93$ and $24.83$ GPa respectively, the former one of which is so far the only theoretical result agreeing with multiple experimental measurements to our best knowledge. The differences between the obtained parameter-free equation of state and those from latest experiments are less than $1.5\%$ in the whole studied pressure range, and particularly, within $0.7\%$ when the applied pressure exceeds over $40$ GPa, the coincidence of which makes us support the argument that the previously observed anharmonicity-driven isostructural phase transition does not exist in the $\beta$-phase even though the thermal effects at room temperature are confirmed to be nontrivial to the phase stability by our quantitative comparisons with the results at $0$K.