Solid solutions of the form, La2/3-xLi3xTiO3 (where x was between 0.03 and 0.167), were investigated by using powder X-ray diffraction, impedance spectroscopy and 7Li nuclear magnetic resonance techniques. A change of symmetry, from tetragonal to orthorhombic, was observed when the Li content was decreased to below x = 0.06. The structural modifications were due mainly to cation vacancy ordering along the c-axis. This gradually disappeared when the Li content was increased. Two Li signals, having different quadrupole constants, were detected in the 7Li nuclear magnetic resonance spectra of orthorhombic/tetragonal perovskites. These were associated with 2 crystallographic sites. In La0.5Li0.5TiO3 which had been prepared by quenching from 1300C into liquid N, a considerable Li mobility was detected in the 7Li nuclear magnetic resonance spectra. In all of perovskites studied, the dependence of the electrical conductivity upon the Li content differed from that expected on the basis of a random distribution of La and Li on A-sites. The direct-current conductivity increased rapidly with the Li content in the orthorhombic samples, but varied much more smoothly in tetragonal ones; where the vacancy distribution became progressively disordered. In all of the present perovskites, the dependence of the direct-current conductivity upon temperature exhibited a non-Arrhenius behaviour; with activation energies of 0.39 and 0.29eV in the 160 to 250 and 250 to 360K ranges, respectively.

Influence of Composition on the Structure and Conductivity of the Fast Ionic Conductors, La2/3-xLi3xTiO3. J.Ibarra, A.Varez, C.Leon, J.Santamaria, L.M.Torres-Martinez, J.Sanz: Solid State Ionics, 2000, 134[3-4], 219-28