State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, People's Republic of China.
J Chem Phys. 2013 Jun 7;138(21):214503. doi: 10.1063/1.4807851.
Magnesium borohydride (Mg(BH4)2) is one of the potential hydrogen storage materials. Recently, two experiments [Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov, and H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011); L. George, V. Drozd, and S. K. Saxena, J. Phys. Chem. C 113, 486 (2009)] found that α-Mg(BH4)2 can irreversibly be transformed to an ultra dense δ-Mg(BH4)2 under high pressure. Its volumetric hydrogen content at ambient pressure (147 g/cm(3)) exceeds twice of DOE's (U.S. Department of Energy) target (70 g/cm(3)) and that of α-Mg(BH4)2 (117 g/cm(3)) by 20%. In this study, the experimentally proposed P4(2)nm structure of δ-phase has been found to be dynamically unstable. A new Fddd structure has been reported as a good candidate of δ-phase instead. Its enthalpy from 0 to 12 GPa is much lower than P4(2)nm structure and the simulated X-ray diffraction spectrum is in satisfied agreement with previous experiments. In addition, the previously proposed P-3m1 structure, which is denser than Fddd, is found to be a candidate of ε-phase due to the agreement of Raman shifts.
硼氢化镁（Mg(BH4)2）是一种有潜力的储氢材料。最近，两项实验[Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov 和 H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011); L. George, V. Drozd 和 S. K. Saxena, J. Phys. Chem. C 113, 486 (2009)]发现，在高压下，α-Mg(BH4)2 可以不可逆地转化为超密的 δ-Mg(BH4)2。其在环境压力下（147 g/cm(3)）的体积储氢量超过了 DOE（美国能源部）目标（70 g/cm(3)）的两倍，也超过了 α-Mg(BH4)2（117 g/cm(3)）的 20%。在这项研究中，实验提出的 δ 相的 P4(2)nm 结构被发现是动态不稳定的。取而代之的是，我们报告了一种新的 Fddd 结构作为 δ 相的良好候选结构。从 0 到 12 GPa 的焓值比 P4(2)nm 结构低得多，模拟的 X 射线衍射谱与之前的实验非常吻合。此外，由于拉曼位移的一致性，之前提出的比 Fddd 更致密的 P-3m1 结构被发现是 ε 相的候选结构。
