  The series Li6.55+xGe0.05La3-xCaxZr1.75Ta0.25O12 ( x= 0, 0.05, 0.10, 0.15,
0.20 ) was prepared by conventional solid state reaction method with the
sintering temperature of 10500C for 7.30 hr by substituting Ca at the La site
to increase the Li ion conductivity. The synergistic effects of Ca
incorporation on Li6.55Ge0.05La3Zr1.75Ta0.25O12 were studied using various
structural and electrochemical analyses. X-ray diffraction, scanning electron
microscopy, and Impedance analysis were used to determine the crystal
structure, morphology, and AC conductivity of the prepared ceramic samples,
respectively. The highest conductivity of 9.95 x 10-4 S/cm was obtained for a
0.05 Ca ceramic sample with minimum activation energy of 0.23 eV. The DC
polarization measurements confirmed the dominance of ionic conduction in 0.05
Ca ceramic. The results obtained make the 0.05 Ca ceramic sample a promising
candidate as solid electrolytes for all solid state Li-ion batteries (ASSLIBs).
