Structural characterization of RNi2 (R ≡ La, Ce) intermetallic compounds and their hydrides

Phase relationships of the La–Ni–Mg system at 500°C from 0 to 66.7at.% Ni

“…The values obtained in this work are larger than the literature ones for corresponding compositions. Although the lattice parameters have not been measured on single-phase samples, they are consistent both with the values published by Kadir et al [25] and Guénée et al [6] for LaNi 4 Mg, and with the literature data for the binary metastable LaNi 2 compound [30,31]. The a value accepted by Oesterreicher and Bitter, proposed by Vogel et al [29] is significantly different and it does not fit perfectly in the regular trend of the RNi 2 phases lattice parameters.…”

Hydrogen absorption–desorption in CeNi2

“…After the absorption-desorption cycles, the diffraction analysis shows a shift of the CeNi 2 peaks, so that the lattice constant decreases from 7.201Å for as-cast alloy to 7.093Å for hydrogenated alloy. A decrease of the lattice constant in hydrogenated CeNi 2 has been already observed [3,4]. It has been associated to the formation of Ce hydrides, which leads to a depletion of Ce in the compound according to the following reaction:…”

“…Ce-Ni system has been widely studied for hydrogen storage properties. In fact, RNi 2 (R = La, Ce) compounds (C15 Laves phase, Mg 2 Cu-type) are of particular interest, since their hydrogen absorption capacity is higher than that of LaNi 5 [3]. CeNi 2 cubic phase easily absorbs up to 4.4 hydrogen-to-compound ratio (H/M) from gaseous hydrogen at room temperature and atmospheric pressure [4].…”

Structural and hydrogen storage properties of LaCaMgNi9-type alloy obtained by mechanical alloying

“…Ni diffraction peaks remain till 20 h and disappear for further durations. After 4 h of milling new peaks appear, characteristic of a ANi 2 phase, crystallizing in a MgCu 2 -type cubic structure [29]. As the refined cell parameter (a = 7.176 Å ) is smaller than that of LaNi 2.17 [7.34(3) Å ] and CaNi 2 [a = 7.25(1) Å ], there is probably a random mixture of La, Ca, and Mg atoms on the A site.…”