Effect of B-site substitution of (Li,La)TiO3 perovskites by di-, tri-, tetra- and hexavalent metal ions on the lithium ion conductivity

Abstract

We report the synthesis and lithium ion conductivity of di-, tri-, tetra- and hexavalent metal ion B-site substituted (Li,La)TiO3(LLT) perovskites. All 5–10 mol% Mg, Al, Mn, Ge, Ru and W ion substituted LLTs crystallize in a simple cubic or tetragonal perovskite structure. Among the oxides investigated, the Al-substituted perovskite La0.55Li0.36□0.09Ti0.995Al0.005O3 (□=vacancy) exhibits the highest lithium ion conductivity of 1.1 × 10−3 S/cm at room temperature which is slightly higher than that of the undoped (Li,La)TiO3 perovskite (8.9 × 10−4 S/cm) at the same temperature. The lithium ion conductivity of substituted LLTs does not seem to depend on the concentration of the A-site ion vacancies and unit cell volume. The high ionic conductivity of Al-substituted LLT is attributed to the increase of the B(Al)-O bond and weakening of the A(Li,La)-O bond. The conductivity behavior of the doped LLT is being described on the basis of Gibbs free energy considerations.