A study of Li2TiOSiO4 and Li2TiOGeO4 by X-ray powder and electron single-crystal diffraction, 17O MAS NMR and O K-edge and Ti L 2,3-edge EELS

Abstract

X-ray powder and electron single-crystal diffraction of crystals of Li2TiOSiO4 and Li2TiOGeO4 showed them to be tetragonal, space group P4/nmm unit-cell parameters a = 6.4379\,(2), c = 4.40032\,(2) Å for Li2TiOSiO4 and a = 6.6110\,(8), c = 4.4372\,(6) Å for Li2TiGeO4. The compounds are isostructural with their sodium analogues but are considerably compressed along the c axis owing to the smaller size of lithium compared with sodium atoms. Square-pyramidal TiO5 groups are joined in these compounds by tetrahedral SiO4 and GeO4 groups, respectively. 17O nuclear magnetic resonance spectra of the two compounds, isotopically enriched with 17O, showed peaks due to the apical titanyl, Ti—O, and basal, bridging, Ti—O—Si or Ti—O—Ge, oxygen atoms of the title compounds. By comparison with reference spectra, oxygen K edges and titanium L 2,3 edges of electron energy-loss spectra were tentatively assigned.