Pressure-induced phase of NaAlH4: A potential candidate for hydrogen storage?

Abstract

The electronic structure and structural stability of the technologically interesting material ${\mathrm{NaAlH}}_4$ are studied using an ab initio projected augmented plane-wave method for different possible structure modifications. We predict that $\mathrm{\alpha -}{\mathrm{NaAlH}}_4$ converts to $\mathrm{\beta -}{\mathrm{NaAlH}}_4$ at 6.43 GPa with a 4 % volume contraction. Both modifications have nonmetallic character with finite energy gaps, the calculated band gap for $\mathrm{\beta -}{\mathrm{NaAlH}}_4$ being almost half of that for the α phase. $\mathrm{\beta -}{\mathrm{NaAlH}}_4$ stores hydrogen more volume efficient than the α phase and would if stabilized at ambient conditions be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency.