Crystal Structure of a Hydride Formed by Electrochemical Hydrogenation in a Ti–Ni–Al Alloy

Abstract

The crystal structure of a Ti–Ni hydride formed by electrochemical hydrogenation in a Ti-48Ni-2Al (at%) alloy has been investigated by electron microscopy and diffraction, and was found to be a bodycentered tetragonal whose lattice parameters were a=0.62 nm and c=1.24 nm, hydrogen atoms being located at (000) and (1/2 1/2 1/2) of the unit cell. Orientation relationship between the parent and hydride lattice was [100]H⁄⁄[100]P, (001)H⁄⁄(001)P. Irrespective of whether the electrochemical hydrogenation was made in the parent state or the martensitic state, the obtained hydrides were identical in crystal structure and similar in morphology. The hydrides remained even after being held for about 3 months at room temperature, and also even after being held for 3.6 ks at 673 K in vacuum (2.0×10−3 Pa). 1/2- extra reflections previously often observed in the parent state of TiNi alloys (including 001/2, 1/2 1/2 0, 1/2 1/2 1/2, and 01/4 2/4 reflections) were found to be due to the formation of the hydrides.