Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada.
J Chem Phys. 2013 Mar 7;138(9):094501. doi: 10.1063/1.4793314.
High-pressure phase transitions in Al2Br6 were theoretically investigated using first principles density functional methods. A structural transformation from the initial molecular solid phase to a planar polymeric phase is predicted near 0.4 GPa that is accompanied with a substantial volume drop. A unique feature of this phase transition is that the hcp lattice of Br atoms remains unchanged during the transition, whereas the Al atoms are displaced from the original tetrahedral sites to the octahedral sites. The calculated phonon spectra indicate that the predicted phase is mechanically stable at 1 atm, and therefore it may be quench-recovered to ambient conditions and exist as a metastable form. A second structural transformation is predicted to occur at around 80 GPa, and also at this point, the AlBr3 reaches a metallic state. The electronic structure of the metallic phase features soft phonon modes and Fermi surface nesting in the Brillouin zone, which leads to localized electron-phonon coupling. By comparing with the experimental data available for high-pressure BI3, the superconducting critical temperature Tc for the metallic phase of AlBr3 is estimated to be at 0.5 K or above.
使用第一性原理密度泛函方法理论研究了 Al2Br6 的高压相转变。在约 0.4 GPa 附近预测到从初始分子固态到平面聚合态的结构转变，伴随着体积的显著下降。这种相变的一个独特特征是，在转变过程中 Br 原子的 hcp 晶格保持不变，而 Al 原子从原始的四面体位置位移到八面体位置。计算得到的声子谱表明，预测的相在 1 大气压下是力学稳定的，因此它可能被淬火恢复到环境条件，并以亚稳形式存在。在大约 80 GPa 预测到第二次结构转变，此时 AlBr3 达到金属态。金属相的电子结构具有软声子模式和布里渊区中的费米面嵌套，导致局域电子-声子耦合。通过与高压 BI3 的实验数据进行比较，估计 AlBr3 金属相的超导临界温度 Tc 在 0.5 K 或以上。
