# Pre-melting hcp to bcc Transition in Beryllium

## TL;DR

This study uses a novel hybrid free energy method to accurately analyze the phase transition of beryllium from hcp to bcc, revealing its occurrence near melting conditions and explaining experimental observation challenges.

## Contribution

It introduces a phonon quasiparticle-based computational framework to study phase stability and transitions in anharmonic materials like beryllium.

## Key findings

- The hcp to bcc transition occurs near the melting curve at 0<P<11 GPa.
- The bcc phase exists in a narrow temperature range that decreases with pressure.
- The method validates a new approach for studying phase transitions in anharmonic systems.

## Abstract

Beryllium (Be) is an important material with wide applications ranging from aerospace components to X-ray equipments. Yet a precise understanding of its phase diagram remains elusive. We have investigated the phase stability of Be using a recently developed hybrid free energy computation method that accounts for anharmonic effects by invoking phonon quasiparticles. We find that the hcp to bcc transition occurs near the melting curve at 0<P<11 GPa with a positive Clapeyron slope of 41 K/GPa. The bcc phase exists in a narrow temperature range that shrinks with increasing pressure, explaining the difficulty in observing this phase experimentally. This work also demonstrates the validity of this theoretical framework based on phonon quasiparticle to study structural stability and phase transitions in strongly anharmonic materials.