Optimization of Lithium Conductivity in La/Li Titanates

Abstract

We have found that for the lanthanum/lithium titanates and related materials with a perovskite-related structure, ABO3, 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 (σ295 K = 2.95 × 10-3 Scm-1). This is La0.56Li0.36□0.08Ti0.97Al0.03O3, the x = 0.03 composition in the solid solution of general formula La0.56Li0.33+x□0.11-xTi1-xAlxO3 (0 ≤ x ≤ 0.06). A similar situation is obtained for x = 0.03 in the related system La0.56-xSrxLi0.33+x □0.11-xTiO3, where σ295 K = 2.54 × 10-3 Scm-1. We have also prepared a material with the highest known conductivity (σ295K = 1.9 × 10-3 Scm-1) in the “classical” La2/3-xLi3x□1/3-2xTiO3 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 ≈√2ap × ≈√2ap × ≈2ap perovskite superstructure.