SYNTHESIS AND STRUCTURE DETERMINATION OF A NEW SERIES OF HYDROGEN STORAGE ALLOYS - RMG2NI9 (R=LA, CE, PR, ND, SM AND GD) BUILT FROM MGNI2 LAVES-TYPE LAYERS ALTERNATING WITH AB(5) LAYERS

A number of new ternary magnesium based alloys, RMg2Ni9 (where R=La, C e, Pr, Nd, Sm and Gd), have been synthesized by reacting a mixture of MgNi2 with RNi5 intermetallic compounds or by direct combination of th e elements in the atomic ratio R:Mg:Ni=1:2:9. The crystal structure, d etermined by Guinier-Hagg X-ray powder diffraction, is related to the hexagonal PuNi3 type. All interatomic distances are close to the corre sponding ones in (C-15) MgCu2, (C-14) MgZn2, (C-36) MgNi2, RNi3 and RN i5 of metallic-type bonding. (C) 1997 Elsevier Science S.A.