Size effect in nanocrystalline lithium-ion conducting perovskite: Li0.3La0.57TiO3

To investigate the nanometer size effect in nanocrystalline lithium-ion conducting perovskite, dense Li0.30La0.57TiO3 ceramic samples with average grain sizes in the range of 25 to 860 nm were prepared by means of the spark plasma sintering. The microstructure of the samples was characterized by TEM, and their electrical properties were investigated by AC impedance spectroscopy as a function of grain size. When the grain size of Li0.30La0.57TiO3 decreases from 860 to 25 nm, the lithium-ion conductivity decreases from 1.9 x 10(-6) to 9.8 x 10(-10) S/cm at 0 degrees C, while the grain boundary conductivity decreases by two to three orders of magnitude. According to the Schottky barrier model, the low grain boundary conductivity can be ascribed to the severe lithium-ion depletion in the space-charge layers. The low grain boundary conductivity, together with the very high grain boundary density, contributes to the significantly decreased lithium-ion conductivity.