Deuterium thermal desorption from Ni-rich deuterated Mg thin films

摘要

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.