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

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) Angstrom for Li2TiOSiO4 and a = 6.6110(8), c = 4.4372 (6) Angstrom 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. O-17 nuclear magnetic resonance spectra of the two compounds, isotopically enriched with O-17, 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,L-3 edges of electron energy-loss spectra were tentatively assigned.