Tittle: Effect of anharmonicity on the hcp to bcc transition in beryllium at high-pressure and high-temperature conditions.
Abstract: We investigate the hcp to bcc phase transition in beryllium (Be) at high-pressure and -temperature (PT) conditions. A recently developed hybrid approach that combines first-principles molecular dynamics and lattice dynamics is used to account for anharmonic contributions to the free energy. Anharmonic effects are shown to be strong at high T in both hcp and bcc Be. They are stronger in hcp Be than in bcc Be, as evidenced by the larger anharmonic vibrational entropy of hcp Be. We find that anharmonicity has a significant influence on the hcp to bcc transition at high-PT conditions. It substantially enlarges the stability domain of hcp Be at high T compared with that calculated under the quasiharmonic approximation (QHA), as a result bringing theoretical predictions into good consistency with recent experimental observations. After considering anharmonic effects, the calculated pressure and temperature of the hcp/bcc/liquid triple point increase from about 85 to 165 GPa, and from about 3300 to 4200 K, respectively, and the predicted Clapeyron slope at the triple point takes a value of −7.4 ± 0.7 K/GPa, noticeably larger in magnitude than previous QHA results in the range of −3 to 2 K/GPa.
Citation: Xian J., Yan J., Liu H., Sun T., Zhang G., Gao X., Song H., (2019). Effect of anharmonicity on the hcp to bcc transition in beryllium at high-pressure and high-temperature conditions. Physical Review B, 99, 064102.
