Lithium ion conductivity in new perovskite oxides [AgyLi1-y](3x)La2/3-x square(1/3-2x)TiO3 (x=0.09 and 0 <= y <= 1)

New perovskite-type lithium ion conductors [AgyLi1-y](3x)La2/3-xTiO3 were s ynthesized and their crystal structure and ionic conductivity were characte rized. The La3+ and vacancies contents have been fixed (x = 0.09) and the s ubstitution of Ag+ for Lif was varied from 0 to 1. The X-ray powder diffrac tion analysis revealed that the symmetry of the doubled-perovskite lattice changes from tetragonal for the nonsubstituted oxide (y = 0) to orthorhombi c when substitution occurs (0 < y < 1), to come back to tetragonal when sub stitution is complete (y = 1). The substitution leads to changes in the bot tleneck sizes and form of the two different A-cages of the structure and co nsequently to the lowest activation energy of the conduction process ever f ound in these titanates (E-a = 0.28 eV for y = 0.5). The immobile ions (La3 + and Ag+) can be considered as obstacles for the lithium motion through th e conduction pathways. Conductivity measurements show that lithium and vaca ncies no longer percolate when the number of immobile ions per Ti in these oxides is greater than 75%. These immobile ions are distributed differently in the two perovskite subcells of the unit cell, leading to an immobile-io ns(La3+/Ag+)-poor layer and an immobile-ions-rich layer. The ionic conducti vity is found to follow the occupancy of the poor layer; that is, the highe r the occupancy, the smaller the lithium conductivity. The lithium motion o ccurs then mainly in the (La3+/Ag+)-poor layer of these oxides.