STRUCTURE OF LA2NIO4.18

The published structure of La2NiO4+y has unusually short (1.94 angstro m) Ni-O bond lengths. We reexamined the structure of La2NiO4.18 using monochromatic synchrotron x-ray radiation. Rietveld refinement of the structure in space group Bbcm yielded Fourier synthesis (F(obs)) maps that suggest a modified structural model for La2NiO4.18. The refined s tructure contains chemically more reasonable interatomic distances (e. g., shortest Ni-O distance of 2.00 angstrom). A comparison of this str ucture with that of the superconductor La2CuO4+y reveals disparities i n the conduction planes of the two materials that may explain differen ces in electrical behavior.