The AB 3 -type LaCaMgNi 9 compound was synthesized using mechanical alloying (MA) starting from elemental La, Ca, Mg, and Ni in the atomic ratio 1:1:1:9. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to study the phase evolution and formation/kinetic mechanism as a function of milling time (4-30 h). The results show multiphase alloys containing LaCaMgNi 9 as a main phase with trigonal PuNi 3 -type structure (R-3m space group) where Ca atoms occupy preferentially the 3a site, while La and Mg atoms occupy the 6c site with a mean composition CaLa 1.2(2) Mg 0.8(2) Ni 9 . The hydrogenation properties of the alloys were examined by solid-gas reaction at room temperature. The PCI curves showed a plateau pressure of 0.25 bar which corresponds to the AB 3 phase. The hydrogen absorption capacity of the AB 3 phase is equal to 5.6 H/u.f AB3 .

The performance of a nickel-metal hydride (Ni-MH) battery mainly depends on the characteristics of the negative electrode. The electrochemical characteristics of mechanically alloyed compound LaCaMgNi 9 , including the discharge capacity and the hydrogen diffusion coefficient, were studied as function of mechanical alloying (MA) conditions. The electrochemical measurements show that the LaCaMgNi 9 electrode has a maximum discharge capacity of about 150 mAh/g at a discharge rate of C/3. The hydrogen discharge capacity dramatically decreases as MA duration exceeds 20 h.