A powder neutron diffraction study of the LaNi4.5Al0.5D4.5 structure at 298 and 77 °K

Abstract

Recently, there has been some controversy over the structure of hydrides of the La(Ni5−xAlx)5 system. One of the proposed structures belongs to the P6/mmm space group and contains five deuterium sites.4,5 The other proposed structure belongs to the P31m space group and contains two deuterium sites.6 In an attempt to resolve this conflict, a powder neutron diffraction study has been carried out for LaNi4.5Al0.5D4.5 at 298 and 77 °K. A modified Rietveld profile analysis technique was used to interpret the data. It is found that a two-site model using P6/mmm symmetry adequately describes the structure at 298 °K. At 77 °K, there is no evidence of magnetic ordering and the structure shows only slight changes from that given at 298 °K. The lattice parameter a contracts from 5.341 to 5.331 Å, while c remains constant at 4.236 Å.