Abstract
The influence of Co substitution on the structural and magnetic properties of NdMgNi4−xCox (x⩽3) alloys and their hydrides has been investigated. The formation of NdMgCo4 compound has not been observed. The gas hydrogenation of these alloys resulted in the formation of NdMgNi4H4, NdMgNi3CoH4.8, NdMgNi2Co2H5.6 and NdMgNiCo3H6.2 hydrides. Transformation from cubic into orthorhombic structure upon hydrogenation has been confirmed for NdMgNi4H4 hydride, whereas it has been found that Co-containing hydrides preserved the parent cubic structure. PC diagrams at 50°C for NdMgNi4−xCox–H2 (x=0, 2, 3) showed only one absorption/desorption plateau, which equilibrium pressure decrease as the cell volume increase. The NdMgCu4 ternary compound has been synthesized, but it does not interact with hydrogen under normal conditions. Electrochemical investigations demonstrated that substitution of the nickel atoms by the cobalt ones in NdMgNi4 does not significantly influence on the maximum discharge capacity (244–261mAh/g) and all alloys are characterized by high cyclic stability. NdMgNi4 and its hydride display a Pauli paramagnet behavior. NdMgNi2Co2 displays a magnetic order below 50K whereas its hydride shows a Pauli paramagnet behavior similar to that of NdMgNi4H4.
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