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

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, A1, 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 La_0.55Li _0.360.09Ti_0.995Al_0.005O₃ (1x1 = vacancy) exhibits the highest lithium ion conductivity of 1.1 x 10 ^-3 S/cm at room temperature which is slightly higher than that of the undoped (Li,La)TiO₃ perovskite (8.9 x 10₄ 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 A1- substituted LLT is attributed to the increase of the B(A1)-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.