Abstract
Mg–Ni multilayers and Ni-rich Mg thin films were deposited by electron gun and pulsed laser deposition, respectively. Samples were submitted to thermal treatment in deuterium or hydrogen atmosphere at 423
K and ∼10
5
Pa pressure to promote the metal to hydride phase transition.
The H chemical bonding in the multilayer samples, after annealing in H
2 atmosphere, was examined by Fourier transform infrared spectroscopy: the obtained spectra suggest that the samples with the Mg:Ni=2:1 atomic ratio contain the Mg
2NiH
4 phase while the samples with lower Ni concentration contain both the MgH
2 and the Mg
2NiH
4 phases.
The effect of the Ni additive on the stability of the deuteride phase was studied by thermal desorption spectroscopy (TDS). The TDS spectra of the single-phase Mg
2NiD
4 samples show a TDS peak at 400
K. The TDS spectra of the two-phase samples show both the D
2 desorption peak at 400
K and a second peak at higher temperature that we attributed to the dissociation of the MgD
2 phase. The high-temperature peak shifts to lower temperatures by increasing the Ni content.
It is suggested that in the two-phase samples, the lattice volumes having the Mg
2Ni structure resulting from the dissociation of the Mg
2NiD
4 phase reduce the thermodynamic stability of the MgD
2 phase.