Synthesis and characterization of novel Li-stuffed garnet-like Li5+2xLa3Ta2-xGdxO12 (0 ≤ x ≤ 0.55): structure-property relationships.

In this article, we report the preparation and characterization of novel Li-stuffed garnets Li5+2xLa3Ta2-xGdxO12 (0 ≤ x ≤ 0.55) for all-solid-state Li ion batteries. The conventional solid-state method was used to prepare Li5La3Ta2O12 in air at 1200 °C and Li5+2xLa3Ta2-xGdxO12 at 1150 °C. Rietveld refinements for the powder X-ray diffraction (PXRD) patterns confirmed the formation of a cubic garnet-like structure (space group Ia3[combining macron]d) with cell constant increased from 12.8176(4) Å (x = 0) to 12.9372(2) Å (x = 0.55). However, small amounts of second phases were observed for higher Gd-doped samples. Scanning electron microscopy revealed that Li5.7La3Ta1.65Gd0.35O12 exhibits the highest density among all investigated samples in this study. The AC impedance spectroscopy data of the samples have been analyzed in relation to ionic conductivity, dielectric constants, and loss tangent. Among the investigated electrolytes, the Li5.7La3Ta1.65Gd0.35O12 composition demonstrated the highest bulk ionic conductivity of 8.18 × 10-5 S cm-1 at 25 °C, which is significantly higher than that of the parent garnet Li5La3Ta2O12 (1.65 × 10-5 S cm-1 at 25 °C). The appearance of a relaxation peak in the loss tangent plots for all samples seems to be due to the dipolar rotations of Li+ ions in Li-stuffed garnets.