Nickel hydride is either an inorganic compound of the formula NiHx or any of a variety of coordination complexes.
Varying the amount of alloying hydrogen and the form of its presence in the nickel hydride (precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting nickel hydride.
[4] In the narrow range of stoichiometries adopted by nickel hydride, distinct structures are claimed.
At room temperature, the most stable form of nickel is the face-centred cubic (FCC) structure α-nickel.
It is a relatively soft metallic material that can dissolve only a very small concentration of hydrogen, no more than 0.002 wt% at 1,455 °C (2,651 °F), and only 0.00005% at 25 °C (77 °F).
The solid solution phase with dissolved hydrogen, that maintains the same structure as the original nickel is termed the α-phase.