  Li$_{7-4x}$Ge$_x$La$_3$Zr$_2$O$_{12}$ has been synthesized using the
conventional solid-state reaction method by substituting Germanium (Ge) at the
Li site, which increases the Li-ion vacancies and leads to an increase in
conductivity with $x$ varying from 0.05-0.20. The formation of cubic phase is
confirmed by using XRD analysis. The surface morphology and elemental
distribution have been studied using SEM characterization which gives the
average particle size of the sample. The densities of the samples were
calculated. For the confirmation of functional groups present within the
sample, IR spectroscopy has been studied. The modulus and ac conductivity
studies have also been studied. A complex impedance study has been done in the
frequency range 20Hz-20MHz. Increase in ionic conductivity by one order has
been observed in the sample with $x=0.10$. The minimum value of 0.56 eV
activation energy is associated with the highest conductivity value of 7.23 x
10$^{-6}$ S/cm at room temperature. Thus increment in ionic conductivity at
room temperature makes this material a promising solid electrolyte for future
sustainable energy storage devices.

Materials Science