Lithium ion conductivity of Li_5+x Ba _x La _3-x Ta₂O₁₂ (x∈=∈0-2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li_5+x Ba _x La_3-x Ta₂O₁₂ (x∈=∈0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data of Li_5+x Ba _x La_3-x Ta₂O₁₂ indicated that single phase oxides with garnet-like structure exist over the compositional range 0≤x≤1.25; while for x∈=∈1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice parameter increases with increasing x and reaches a maximum at x∈=∈1.25 then decreases slightly with further increase in x in Li _5+x Ba _x La_3-x Ta₂O₁₂. The impedance plots of Li_5+x Ba _x La_3-x Ta ₂O₁₂ samples obtained at 33 °C indicated a minimum grain-boundary resistance (R _gb) contribution to the total resistance (R _b∈+∈R _gb) at x∈=∈1.0. The total (bulk∈+∈grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches a maximum at x∈=∈1.25 and then decreases with further increase in x in Li_5+x Ba _x La _3-x Ta₂O₁₂. Scanning electron microscope investigations revealed that Li_6.25Ba_1.25La _1.75Ta₂O₁₂ is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li _6.25Ba_1.25La_1.75Ta₂O₁₂ exhibits the highest total (bulk∈+∈grain boundary) and bulk ionic conductivity of 5.0∈×∈10^-5 and 7. 4∈×∈10^-5 S/cm at 33 °C, respectively.