Structural Characterization of the Engineered Scavenger Compound, H-Li2Ti3O7

The so-called H phase in the system Li2O-TiO2 was prepared from niobia-doped R-Li2Ti3O7 (ramsdellite form) by reheating the quenched metastable R phase to 1000 K. The phase was characterized using transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and powder neutron diffraction (ND). It has trigonal symmetry, space group R c, with hexagonal cell parameters a=5.0744(1) ? and c=69.9405(3) ? at 303 K. The unit cell composition is Li28.5Ti36.5Nb1.1O90. High-resolution TEM images were used to establish a starting model for the structure, which was refined by the Rietveld method using ND data collected at 1.5 K, to Rwp=5.8%, RB=2.0% (350 reflections). The structure comprises an ordered intergrowth, parallel to (001) of blocks of corundum-type [Ti2O3]2+ and LiNbO3-type structures. The Li atoms in the centre of the LiNbO3-type blocks have triangular coordination as in paraelectric LiNbO3. The effect of temperature on the structure was studied by Rietveld refinement of XRD data sets collected between 100 and 1173 K. The relationship to the structure of the R phase is discussed.