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 LiBe 2 H 5 and LiBeH 5 with higher GHD synthesizable at high pressures by using a first-principles CALYPSO technique on crystal structure prediction. It was found that LiBe 2 H 5 and LiBeH 5 become thermodynamically stable above 228 and 67 GPa, respectively, with respect to various decomposition routes. In their stable states, LiBe 2 H 5 adopts a layered ionic I 4/ mcm structure, characterized by Li + cations together with negatively charged polymeric networks consisting of BeH 8, while LiBeH 5 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 BeH 2 . In contrast with the stubborn insulating character of the Li n Be m H n +2 m systems ( n and m are integers, e.g., LiBeH 3, Li 2 BeH 4, and LiBe 2 H 5 ), the metallization of LiBeH 5 and BeH 2 takes place at high pressures and their structures experience either a strengthening of covalency in LiBeH 5 within the H 3 – units or a weakening of ionic character in BeH 2 due to the missing of low-electronegativity lithium atom. Our findings quest future experiments to synthesize these high GHD hydrogen-storage materials.