Crystal chemistry of NpNi5 compound

The compound, NpNi5, was prepared and its crystal properties studied by means of powder X-ray diffraction. The existence and properties of this compound were pursued as they are important in developing further the Np-Ni phase diagram. The crystal symmetry of this material was determined to be hexagonal and have the D2d CaCu5 structure type, which is also observed for ThNi5 and PuNi5. The lattice parameters of NpNi5 were calculated to be: ao=0.4859±0.0002 and co=0.3991±0.0003 nm. Based on these lattice parameters and the apparent radius of Np in the NpNi5 compound, it appears that Np can be considered as being tetravalent, which has certain bonding implications. The apparent valence states for Np and other actinides in these actinide-Ni5 compounds are discussed, as well as the variation in cell volumes noted for the known actinide- and lanthanide-Ni5 compounds. (orig.)