Lithium ion conductivity of Li5+xBaxLa3-xTa2O12 (x=0-2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li5+xBaxLa3-xTa2O12 (X=O, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with gamet-like structure were studied. The powder X-ray diffraction data of Li5+xBaxLa3-xTa2O12 indicated that single phase oxides with gamet-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 Li5+xBaxLa3-xTa2O12. The impedance plots of Li5+xBaxLa3-xTa2O12 samples obtained at 33 degrees 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 Li5+xBaxLa3-xTa2O12. Scanning electron microscope investigations revealed that Li6.25Ba1.25La1.75Ta2O12 is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li6.25Ba1.25La1.75Ta2O12 exhibits the highest total (bulk+grain boundary) and bulk ionic conductivity of 5.0 x 10(-5) and 7.4 x 10(-5) S/cm at 33 degrees C, respectively.