STRUCTURE OF 2 DISORDERED MOLYBDATES, (LI2MOO3)-O-IV AND (LI4MO3O8)-O-IV NEUTRON-SCATTERING

The structures of the disordered lithium molybdates Li2MoO3 and Li4Mo3 O8 have been investigated using total neutron scattering from polycrys talline powders. Rietveld analysis of the Bragg scattering is used to determine the average structures. Shortcomings in this method of analy sis are demonstrated by comparing the total correlation function, T(r) , determined from total neutron scattering, with those calculated from the structures determined from Rietveld analysis. Much more satisfact ory models for these materials are derived from the structurally relat ed ordered material LiZn2Mo3O8, using information from Mo K-edge exten ded X-ray absorption fine-structure spectroscopy (EXAFS). These models include metal-metal-bonded Mo3O13 clusters [d(Mo-Mo) = 2.58 Angstrom in Li2MoO3 and 2.56 Angstrom in Li4Mo3O8] not present in the average s tructure determined from Rietveld analysis [d(Mo-Mo) = 2.88 Angstrom i n Li2MoO3]. In contrast to EXAFS studies neutron diffraction yields in formation on all the pair correlations in the material, not merely tho se involving molybdenum, and allows, for example, the location of Lith ium. Remaining discrepancies between our models and the experimental T (r)'s give an insight into the disorder in the two materials.