An extended x-ray absorption fine structure study of hydrogen storage in Ti–Hf–Ni alloys

Abstract

The effect of hydrogenation on the local structure of a Ti40Hf40Ni20 crystalline alloy was studied by means of the extended x-ray absorption fine structure. The samples were loaded to different hydrogen-to-metal ratios, H/M, between 1.2 and 1.7. The desorption process was also investigated by studying the local order in an alloy charged to H/M = 1.85 then desorbed to H/M = 0.8. For the non-hydrogenated alloys, the local order was very similar in Ti–Hf–Ni and Ti–Zr–Ni alloys, quasicrystal or crystal. With increasing hydrogen concentration, all of the mean interatomic distances increased, except for the Ni–Hf (Hf–Ni) ones, which show an anomalous behaviour, decreasing with increasing H/M. This leads to a remarkable inversion of the atomic subshells of titanium and nickel in the first environment of hafnium atoms around H/M = 1.2. The increase of distances is a maximum for the Ti–Ti and the Ti–Hf correlations, which is consistent with the hydrogen atoms sitting preferentially near titanium and hafnium atoms. Similar conclusions were obtained previously from a study of Ti–Zr–Ni alloys.