Order–disorder of the A-site ions and lithium ion conductivity in the perovskite solid solution La0.67−xLi3xTiO3 (x=0.11)

Abstract

The A-site-deficient perovskite solid solution (ADPESS) La0.67−xLi3xTiO3 (x=0.11) underwent an order–disorder transition reversibly with a reversible change in ionic conductivity. The cubic, disordered form (a=ap) was obtained by quenching from temperatures above ∼1150°C, while the tetragonal, ordered form (a=ap, c≈2ap), by annealing at temperatures below ∼1150°C. Since controlled thermodynamically, the extent of ordering of La ions could be changed reversibly by annealing in a range of 600–1150°C. The equilibrated order parameter S increased continuously from 0 at 1150°C to ∼0.83 at 600°C with decreasing annealing temperature. The bulk ionic conductivity at 25°C had a small maximum at S≈0.2 and decreased increasingly rapidly with increasing extent of ordering in a range of S>0.2. The tetragonal distortion of the subcell began at S≈0.2. The distortion became more manifest and the lattice parameters a contracted more with increasing extent of ordering in a range of S>0.2. The decrease in ionic conductivity is attributed to an increase in activation energy for ionic conduction, which is presumably associated with the contraction of the lattice parameter a of the subcell.