Deuteration properties of CaNi5−xCux system

Intermetallic compounds with nominal formula CaNi5−xCux (x = 0, 1, 2.5) have been prepared in order to investigate their hydrogenation properties. The samples were obtained by arc-melting and were deuterated in a Sieverts reactor. For x = 0 and 1, we have found that the fast kinetics and the different shape of the curve (non sigmoidal) in the second absorption process indicate an improvement of the hydrogen absorption due to the activation of the alloys. The deuterium desorption spectra are similar for x = 0 and 1 whereas for x = 2.5 the desorption ranges a broader temperature interval (∼100–350 °C) indicating a certain degree of chemical inhomogeneity or amorphization intrinsic to the parent sample or induced by the deuterium absorption. The formed deuterides were passivated in the presence of air in order to carry out a neutron diffraction study, allowing us to determine the deuterium positions in the samples. While in CaNi4CuDy the deuterium is randomly distributed over seven different positions, in CaNi5Dy the deuterium only occupies five of them. This wider distribution in CaNi4CuDy can explain its higher stability, and therefore, its higher desorption temperature for deuterium.