Structural investigations of migration pathways in lithium ion-conducting La2/3−xLi3xTiO3 perovskites

The average structure and microstructure of a lithium-ion conducting perovskite La2/3−xLi3xTiO3 (x = 0.12) were investigated using neutron diffraction and transmission electron microscopy (TEM). The obtained results were compared with those of previous studies on La2/3−xLi3xTiO3 series compounds, and the relationship between their structures and ionic conduction was discussed. The Rietveld refinement using neutron diffraction data reveals that the average structure (space group: Cmmm) of furnace-cooled Li-rich La2/3−xLi3xTiO3 (x = 0.12) involves alternative ordered arrangement of La along the c-axis and anti-phase-tilt of TiO6 octahedra along the b-axis as with Li-poor La2/3−xLi3xTiO3(x = 0.05). It was found that the strong correlation between structure and percolative diffusion pathways in the perovskites is primarily referred to the ordered arrangement of La ions, and the “bottleneck” square—surrounded by four oxygen ions determined by the distortion and tilt of TiO6 octahedra. In addition, the 90°-oriented micro-domain structure, which also influences the percolative diffusion pathways in La2/3−xLi3xTiO3, was observed by TEM.