Impedance and Equivalent Circuit Analysis of Li7La3Zr1.5Sn0.5O12 Ceramics

High-purity Li₇La₃Zr_1.5Sn_0.5O₁₂ samples that formed with garnet-type crystal structure were prepared using biopolymer sol-gel method. X-ray diffraction shows that Li₇La₃Zr_1.5Sn_0.5O₁₂ formed a tetragonal phase with a space group of I4₁/acd) at 1000°C. Then, the crystal symmetry transformed to a cubic phase with a space group of Ia-3m at 1100°C. Impedance spectroscopy analysis was used to determine the electrical properties of Li₇La₃Zr_1.5Sn_0.5O_12. Equivalent circuit analysis was performed to distinguish microscopic contribution in the samples. The impedance data were accurately fitted to the impedance data measured from 120°C to 210°C with the equivalent circuit analysis contributed by bulk and grain boundary effects. The Arrhenius plots show a change of slope with different activation energies for low- and high-temperature regions, which is contributed to by order-disorder transitions that affect the mobility of Li⁺ ions. The heterogeneity of the sample was observed from Z′ and M″ spectroscopic plots. The SEM micrographs reveal that a large grain size was obtained in the Li₇La₃Zr_1.5Sn_0.5O₁₂ samples.