The A-site deficient perovskite solid solution, La0.56Li0.33TiO3, underwent a reversible order-disorder transition, with a reversible change in ionic conductivity. The cubic disordered form was obtained by quenching from temperatures above about 1150C, while the tetragonal ordered form was obtained by annealing at temperatures below about 1150C. The extent of ordering of the La ions could be reversibly changed by annealing at temperatures of between 600 and 1150C. The equilibrated order parameter increased continuously, from 0 at 1150C to 0.83 at 600C, with decreasing annealing temperature. The bulk ionic conductivity at 25C exhibited a small maximum at an equilibrated order parameter of about 0.2, and decreased more and more rapidly with further increases in the extent of ordering. Tetragonal distortion of the sub-cell began at an equilibrated order parameter of 0.2. The distortion became more evident, and the lattice parameters contracted more, with increasing extent of ordering. The decrease in ionic conductivity was attributed to an increase in the activation energy for ionic conduction; and this in turn was attributed to the contraction of the lattice parameter of the sub-cell.

Order-Disorder of the A-Site Ions and Lithium Ion Conductivity in the Perovskite Solid Solution (La,Li,Ti)O3. Y.Harada, Y.Hirakoso, H.Kawai, J.Kuwano: Solid State Ionics, 1999, 121[1-4], 245-51