The A-site-deficient perovskite solid solution (ADPESS) La 0.67−x Li 3x TiO 3 (x=0.11) underwent an order–disorder transition reversibly with a reversible change in ionic conductivity. The cubic, disordered form (a=a p) was obtained by quenching from temperatures above ∼1150 C, while the tetragonal, ordered form (a=a p, c≈2a p), by …