High-energy X-ray and neutron diffraction measurements on polycrystalline La2/3 − xLi3xTiO3 (0.075 < x < 0.165) were performed. The total scattering structure factors were analysed by the reverse Monte Carlo modelling technique, resulting in three-dimensional particle configurations. These configurations were then used for revealing the distributions of La and Li ions and to understand the relationship between these distributions and ionic conduction. An alternating arrangement of La-rich and La-poor layers along the c-axis was found in the x = 0.075 composition. Intriguingly, this arrangement had gradually disappeared in samples with higher Li concentration. Furthermore, reverse Monte Carlo models exhibited disordered distributions of Li ions, situated mainly on the La-rich layer, and there was a significant probability of Li ions occupying the interstitial sites (T site) between the O-3 triangle plane of the TiO6 octahedron and an La ion or its vacancy site. It was also found on the basis of the reverse Monte Carlo models that the bond valence sum for Li ions behaves differently on La-rich and La-poor layers at low Li concentration compositions, but they were similar at high Li concentration compositions. This was consistent with the behaviour of the alternating arrangement of La-rich and La-poor layers. It was also suggested that the Li ions around the bottleneck at (1/2, 0, 0) (bottom layer) could jump to an adjacent bottleneck at (0, 1/2, 0) through the T site and not only Li ions in the La-poor layers but also Li ions in the La-rich layers contributed to the bottleneck–bottleneck Li conduction.

Structural Disorder in Lithium Lanthanum Titanate: the Basis of Superionic Conduction. K.Ohara, Y.Kawakita, L.Pusztai, L.Temleitner, S.Kohara, N.Inoue, S.Takeda: Journal of Physics - Condensed Matter, 2010, 22[40], 404203