Pre-melting hcp to bcc Transition in Beryllium

Beryllium (Be) is an important material with wide applications ranging from aerospace components to x-ray ray equipment. 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 → bcc transition occurs near the melting curve at 0 < P < 11 GPa with a positive Clapeyron slope of 41(4) K/GPa, a result that is more consistent with recent experimental measurements. This work also demonstrates the validity of this theoretical framework based on the phonon gas model and phonon quasiparticle to study phase transitions in strongly anharmonic materials.