Effect of anharmonicity on the hcp to bcc transition in beryllium at high-pressure and high-temperature conditions
Effect of anharmonicity on the hcp to bcc transition in beryllium at high-pressure and high-temperature conditions
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高压高温条件下非谐性对铍 hcp 到 bcc 转变的影响
DOI：
10.1103/physrevb.99.064102
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发表时间：
2019
影响因子：
3.7
通讯作者：
Hai-Feng Song
中科院分区：
文献类型：
--
作者：
Jia-Wei Xian;Jun Yan;Hai-Feng Liu;Tao Sun;Gong-Mu Zhang;Xing-Yu Ga;Hai-Feng Song
本文研究了高温高压下铍的hcp到bcc相变。最近开发的混合方法，结合第一性原理分子动力学和晶格动力学是用来考虑非谐贡献的自由能。非谐效应在hcp和bcc Be的高强度下都很强。他们是更强的hcp Be比体心立方Be，证明了较大的非谐振动熵的hcp Be。我们发现在高条件下，非谐性对hcp到bcc的转变有显著的影响。与准谐波近似（QHA）计算的结果相比，它大大扩大了hcp Be在高温下的稳定域，使理论预测与最近的实验观测结果符合得很好.在考虑非谐效应后，计算的hcp/bcc/liquid三相点的压力和温度分别从85 ~ 165 GPa和3300 ~ 4200 K增加，预测的Clapeyron斜率在三相点处的值为，明显大于以前QHA在~ 2 K/GPa范围内的结果。
We investigate the hcp to bcc phase transition in beryllium (Be) at high-pressure and -temperature () 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 highin 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-conditions. It substantially enlarges the stability domain of hcp Be at highcompared 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, noticeably larger in magnitude than previous QHA results in the range ofto 2 K/GPa.