中国物理B ›› 2012, Vol. 21 ›› Issue (8): 86104-086104.doi: 10.1088/1674-1056/21/8/086104

• CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES • 上一篇    下一篇

High volumetric hydrogen density phases of magnesium borohydride at high-pressure: A first-principles study

范靖, 包括, 段德芳, 汪连城, 刘冰冰, 崔田   

  1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
  • 收稿日期:2011-12-12 修回日期:2012-01-26 出版日期:2012-07-01 发布日期:2012-07-01
  • 基金资助:
    Project supported by the National Basic Research Program of China (Grant No. 2011CB808200), the National Natural Science Foundation of China (Grant Nos. 51032001, 11074090, 10979001, and 51025206), and the Funds for Changjiang Scholar and Innovative Research Team in University (Grant No. IRT1132).

High volumetric hydrogen density phases of magnesium borohydride at high-pressure: A first-principles study

Fan Jing (范靖), Bao Kuo (包括), Duan De-Fang (段德芳), Wang Lian-Cheng (汪连城), Liu Bing-Bing (刘冰冰), Cui Tian (崔田)   

  1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
  • Received:2011-12-12 Revised:2012-01-26 Online:2012-07-01 Published:2012-07-01
  • Contact: Cui Tian E-mail:cuitian@jlu.edu.com
  • Supported by:
    Project supported by the National Basic Research Program of China (Grant No. 2011CB808200), the National Natural Science Foundation of China (Grant Nos. 51032001, 11074090, 10979001, and 51025206), and the Funds for Changjiang Scholar and Innovative Research Team in University (Grant No. IRT1132).

摘要: The previously proposed theoretical and experimental structures, bond characterization, and compressibility of Mg(BH4)2 in a pressure range from 0 to 10 GPa are studied by ab initio density-functional calculations. It is found that the ambient pressure phases of meta-stable I41/amd and unstable P-3m1 proposed recently are extra stable and cannot decompose under high pressure. Enthalpy calculation indicates that the ground state of F222 structure proposed by Zhou et al. [2009 Phys. Rev. B 79 212102] will transfer to I41/amd at 0.7 GPa, and then to P-3m1 structure at 6.3 GPa. And the experimental P6122 structure (α-phase) transfers to I41/amd at 1.2 GPa. Furthermore, both I41/amd and P-3m1 can exist as high volumetric hydrogen density phases at low pressure. Their theoretical volumetric hydrogen densities reach 146.351 g H2/L and 134.028 g H2/L at ambient pressure respectively. The calculated phonon dispersion curve shows that the I41/amd phase is dynamically stable in a pressure range from 0 to 4 GPa and the P-3m1 phase is stable at pressures higher than 1 GPa. So the I41/amd phase may be synthesized under high pressure and retained to ambient pressure. Energy band structures show that both of them are always ionic crystalline and insulating with a band gap of about 5 eV in this pressure range. In addition, they each have an anisotropic compressibility. The c axis of these structures is easy to compress. Especially, the c axis and volume of P-3m1 phase are extraordinarily compressible, showing that compressing alone c axis can increase the volumetric hydrogen content for both I41/amd and P-3m1 structures.

关键词: hydrogen storage material, metal borohydride, thermodynamic stability, dynamical stability

Abstract: The previously proposed theoretical and experimental structures, bond characterization, and compressibility of Mg(BH4)2 in a pressure range from 0 to 10 GPa are studied by ab initio density-functional calculations. It is found that the ambient pressure phases of meta-stable I41/amd and unstable P-3m1 proposed recently are extra stable and cannot decompose under high pressure. Enthalpy calculation indicates that the ground state of F222 structure proposed by Zhou et al. [2009 Phys. Rev. B 79 212102] will transfer to I41/amd at 0.7 GPa, and then to P-3m1 structure at 6.3 GPa. And the experimental P6122 structure (α-phase) transfers to I41/amd at 1.2 GPa. Furthermore, both I41/amd and P-3m1 can exist as high volumetric hydrogen density phases at low pressure. Their theoretical volumetric hydrogen densities reach 146.351 g H2/L and 134.028 g H2/L at ambient pressure respectively. The calculated phonon dispersion curve shows that the I41/amd phase is dynamically stable in a pressure range from 0 to 4 GPa and the P-3m1 phase is stable at pressures higher than 1 GPa. So the I41/amd phase may be synthesized under high pressure and retained to ambient pressure. Energy band structures show that both of them are always ionic crystalline and insulating with a band gap of about 5 eV in this pressure range. In addition, they each have an anisotropic compressibility. The c axis of these structures is easy to compress. Especially, the c axis and volume of P-3m1 phase are extraordinarily compressible, showing that compressing alone c axis can increase the volumetric hydrogen content for both I41/amd and P-3m1 structures.

Key words: hydrogen storage material, metal borohydride, thermodynamic stability, dynamical stability

中图分类号:  (Crystallographic aspects of phase transformations; pressure effects)

  • 61.50.Ks
62.50.-p (High-pressure effects in solids and liquids) 63.20.D- (Phonon states and bands, normal modes, and phonon dispersion) 71.20.-b (Electron density of states and band structure of crystalline solids)