Neutron and X-ray powder diffraction studies of LiMn2-yCryO4

The crystal structures of chromium-doped spinel-type lithium manganese oxides, LiMn2-yCryO4 (y = 0, 1/9, 1/6, and 1/3), have been studied by neutron and X-ray powder diffraction. Rietveld refinements of their neutron diffraction data revealed that Cr is substituted for Mn selectively and that Li occupies only the 8a site. Thus, the above solid solutions can be expressed as Li(Mn2-yCry)O-4. The fractional coordinates of oxygen were almost the same in all the samples while the lattice parameter a decreased linearly with increasing Cr content. The lengths of (Mn, Cr)-O bonds in (Mn, Cr)O-6 octahedra changed in a manner expected from average ionic radii for Mn2-yCry. Rietveld analyses of the X-ray diffraction data showed the crystallite size and anisotropic strain to decrease with increasing Cr content. (C) 1999 Academic Press.