Evolution of the local structure with hydrogenation in Ti-Zr-Ni quasicrystals and approximants

The effect of hydrogenation on the local structure of Ti-Zr-Ni alloys has been studied by means of extended x-ray absorption fine structure. The alloys were either icosahedral quasicrystals or crystalline approximants. They were loaded to different hydrogen-to-metal ratios 1.2 ≤ H/M ≤ 1.7. The desorption process was also investigated by studying the local order in an alloy charged to H/M = 1.2 then desorbed to H/M = 0.84. The local structure was identical in the crystalline and quasicrystalline alloys with the same H/M ratio (0 or 1.2) and that of the desorbed sample was intermediate between that of the non-hydrogenated samples and that of the samples charged to 1.2. Therefore, it is possible to follow the evolution of the local structure with hydrogenation from H/M = 0 to 1.7. A general increase of all the mean first distances was found except for the Zr-Ni (Ni-Zr) one. There is a remarkable inversion of the atomic subshells of titanium and nickel in the first environment of zirconium atoms around H/M = 1. For the 1.56 hydrogenated sample, the effect of adding a small amount of lead, which stabilizes the icosahedral phase, was studied and it was demonstrated that lead atoms substitute for the nickel atoms and are, therefore, incorporated into the quasilattice.