The Preferable F2dd Phase for Ca(BH4)2 Crystal Under Hydrostatic Pressures

• DOI: 10.1007/s11664-016-5241-7
• Publication Date: 2017-02-10T16:57:27Z
• Authors: Tuan Le; Phu Manh Do
• Keywords: 0103 physical sciences; 7. Clean energy; 01 natural sciences

Calcium borohydride (Ca(BH4)2) belongs to a series of widely spread, cheap metal borohydrides that are promising for the mobile hydrogen economy, but with some properties still in open discussions. In particular, for the experimental Ca(BH4)2 α-phase both space groups F2dd and Fddd have been proposed. This work presents the analysis of enthalpy and bonding length changes in Ca(BH4)2 over the hydrostatic pressure range of 0–40 GPa, which shows a preference for the F2dd phase of Ca(BH4)2 over the Fddd one. The validity of the calculations, based on density functional theory implemented by the ABINIT package with the GGA method, is supported by the accordance of the results with experimental data for the α′-, β-, and δ-phases of Ca(BH4)2. The phonon spectra show the stability of the Ca(BH4)2 phases, where B- and H-ions provide the dominant part of the optical phonon bands, whereas the Ca-, B-, H-ions contribute to the acoustic bands.