Interstitial metal hydrides

Hydrogen atoms are small enough to occupy the interstitial holes in a metal lattice and the absorption of H₂ by a variety of metals (and also alloys) leads to the formation of metal hydrides in which hydrogen atoms reside in interstitial cavities, interstitial metal hydrides. For example, nonstoichiometric hydrides TiH_1.7, HfH_1.98 and HfH_2.10 are formed when titanium and hafnium react with H₂. Niobium forms a series of non-stoichiometric hydrides of formula NbHx (0 < x ≤ 1) and at low hydrogen content, the bcc structure of Nb metal is retained. An interesting property of these metal hydrides is their ability to release hydrogen upon heating, and this leads to their use as ‘hydrogen storage vessels.