Optimization of Lithium Conductivity in La/Li Titanates

We have found that for the lanthanum/lithium titanates and related materials with a perovskite-related structure, ABO 3, optimum lithium conductivity takes place for a particular concentration of A-cation vacancies (□) equal to 8%. We have prepared a new oxide with the highest lithium conductivity reported to date for a crystalline material (σ 295 K = 2.95 × 10 - 3 Scm - 1 ). This is La 0.56 Li 0.36 □ 0.08 Ti 0.97 Al 0.03 O 3, the x = 0.03 composition in the solid solution of general formula La 0.56 Li 0.33+ x □ 0.11 - x Ti 1 - x Al x O 3 (0 ≤ x ≤ 0.06). A similar situation is obtained for x = 0.03 in the related system La 0.56 - x Sr x Li 0.33+ x □ 0.11 - x TiO 3, where σ 295 K = 2.54 × 10 - 3 Scm - 1 . We have also prepared a material with the highest known conductivity (σ 295K = 1.9 × 10 - 3 Scm - 1 ) in the “classical” La 2/3 - x Li 3 x □ 1/3 - 2 x TiO 3 system and it also corresponds to the same A-cation deficiency. Optimization of Li conductivity requires then both the control of the charge carriers/vacancies ratio as well as shortening of the B−O distances or increasing of the A−O distances. 3-D microtwinning is observed in the crystals of all these oxides, which have a ≈√2 a p × ≈√2 a p × ≈2 a p perovskite superstructure.