Crystal structure of nonstoichiometric copper-substituted La(Ni1-zCuz)(x) compounds studied by neutron and synchrotron anomalous powder diffraction

The structural properties of the potential battery electrode materials LaNi 4Cu, LaNi4.4Cu, LaNi5Cu, and LaNi4.5Cu1.5 hare been investigated by neutron and anomalous synchrotron powder diffraction. The nonstoichiometry of such AB(x) (5 less than or equal to x less than or equal to 6) compounds has be en described in a structure derived from the hexagonal CaCu5-type structure by replacement of the A atoms by dumbbells of B atoms. In these copper-sub stituted compounds, Cu can occupy any of the four available nickel sites. F rom a joint refinement procedure using both neutron and synchrotron data, t he copper-to-nickel ratio at each B site has been determined. This shows th at substitution is not random and that copper occupies some crystallographi c sites preferentially. The results are discussed and compared to other sub stituted AB(5) systems. (C) 1999 Academic Press.