Exploring High-Pressure Lithium Beryllium Hydrides: A New Chemical Perspective

Lithium beryllium hydrides are known as high gravimetric hydrogen density (GHD) hydrogen-storage materials. However, the lithium beryllium hydrides that can be experimentally synthesized remain scarce. Here we report a computer design on novel hydrides of LiBe2H5 and LiBeH5 with higher GHD synthesizable at high pressures by using a first-principles CALYPSO technique on crystal structure prediction. It was found that LiBe2H5 and LiBeH5 become thermodynamically stable above 228 and 67 GPa, respectively, with respect to various decomposition routes. In their stable states, LiBe2H5 adopts a layered ionic I4/mcm structure, characterized by Li+ cations together with negatively charged polymeric networks consisting of BeH8, while LiBeH5 takes hydrogen sublattices composed of either H-2 molecules or H-3(-) structural units. The nature and the strength of covalent and ionic bonding of these stable states were identified and analyzed to compare with the high pressure structures of BeH2. In contrast with the stubborn insulating character of the LinBemHn+2m systems (n and m are integers, e.g., LiBeH3, Li2BeH4, and LiBe2H5), the metallization of LiBeH5 and BeH2 takes place at high pressures and their structures experience either a strengthening of covalency in LiBeH5 within the H-3(-) units or a weakening of ionic character in BeH2 due to the missing of low-electronegativity lithium atom. Our findings quest future experiments to synthesize these high GHD hydrogen-storage materials.