Abstract: In the current work, we studied the effect of Ga+3 substitutions on the Ta+5 sites in
Li5+2xLa3Ta2-xGaxO12 (LLT-Ga) lithium conducting garnets (with x = 0.1–0.5) in order to enhance the
ionic conductivity of these materials. The current materials are prepared by solid state reaction and
their electrical properties are studied by impedance spectroscopy measurements. XRD data showed
that cubic garnet phases are obtained for LLT-Ga garnets. The ionic conductivity increased by one
order of magnitude for x = 0.3 composition with a value of ~4 10􀀀5 S/cm compared to that of
Li5La3Ta2O12 material. Moreover, the hopping frequency and the concentration of mobile Li+ ions
were estimated from analysis of the conductivity spectra, and it was found that both the concentration
and mobility of Li+ ions increased with increasing Ga+3 content in the materials. The dielectric and
relaxation properties were studied in the dielectric permittivity and electric modulus formalisms.
The current materials exhibited giant values of the dielectric constant of "0 ~ 6500, originating from
internal effects in the materials.