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

The electronic structure and structural stability of the technologically interesting material NaAlH4 are studied using an ab initio projected augmented plane-wave method for different possible structure modifications. We predict that alpha-NaAlH4 converts to beta-NaAlH4 at 6.43 GPa with a 4 % volume contraction. Both modifications have nonmetallic character with finite energy gaps, the calculated band gap for beta-NaAlH4 being almost half of that for the alpha phase. beta-NaAlH4 stores hydrogen more volume efficient than the alpha phase and would if stabilized at ambient conditions be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency. (C) 2003 American Institute of Physics.