Effect of average and local structures on lithium ion conductivity in La2/3−xLi3xTiO3

Abstract

In order to investigate lithium ion conduction mechanism of the lithium ion–conducting perovskite oxides, La_2/3−xLi_3xTiO₃ (x = 0.06–0.15) (LLT), their average structure, local structure and lithium ion conductivity were analyzed. We applied Rietveld analysis with X-ray diffraction for discussing the average structure of LLT with disordered (high temperature phase, HT) and ordered (low temperature phase, LT) A-site ion arrangements along the c-axis of its orthorhombic lattice. Synchrotron X-ray absorption fine structure (XAFS) analysis was also measured for considering local structures. Differences for lithium ion migration caused by A-site ion ordering or change of lithium ion concentration are well-explained by the atomic positions and Coulombic interactions among the lithium and surrounding ions. The local inter-atomic distances were estimated by extended XAFS (EXAFS), as well as Debye Waller factors that reflect local distortion around the ions of interest. Consideration on these local structure features and the activation energy for the lithium ion conduction indicates that the lithium ion conductivity is governed by the Coulombic repulsion force between the lithium ion and the titanium ion, and/or the bottleneck distortion in the lithium ion channels consisted of four oxygen ions.