Lithium ion conduction in Li5La3Ta2O12 and Li7La3Ta2O13 garnet-type materials

Electrical properties of the lithium garnets Li₅La₃Ta₂O₁₂ (L5LTO) and Li₇La₃Ta₂O₁₃ (L7LTO) are reported over a wide frequency range from 10 MHz to 0.1 Hz at different temperatures. The structural properties are characterized by powder X-ray diffraction, Scanning electron microscopy with energy dispersive X-ray spectroscopy and Fourier transformation Infrared spectroscopy. By means of the frame work of classical brick layer model (BLM) and of a finite element approach, the ion transport properties of grain and grain boundary for the lithium garnets were analyzed. The specific grain conductivity of 5.0?×?10^?6?S/cm at 40 °C is found for both lithium garnets. Specific grain conductivities and grain boundary conductivities are thermally activated, with activation energies found to be in the range of 0.55–0.61 eV. The total conductivity is found to be depending on the ion conduction of grain boundary. The information on the fraction of contact area α_contact between grains <0.25 is obtained by the finite element approach for Li₇La₃Ta₂O₁₃.