The role of Li site occupancy on the Li-ion conductivity of Ta-doped Li6.75La3Zr1.75Ta0.25O12 solid electrolyte materials with high Li concentrations

Garnet-type Li7La3Zr2O12 has attracted much attention because of its promising properties of high ionic conductivity, good chemical stability against Li metal, and good mechanical strength. To better understand the Li conduction mechanism, the Li site occupancy and Li-ion conductivity are studied with a high Li concentration in the range of 6.70–7.15 mol per formula unit. Aluminum and silicon, which presumably were transferred to the sample from the Al2O3 crucible during processing, were included in the cubic garnet structure for the Rietveld refinements. The Li-ion conductivity increases with the occupancy of the octahedral Li site (Occupancy: 0.78–0.87, Li-ion conductivity: 3–5 × 10−4 S/cm). As the lithium content increases, the portion of lithium occupying the 96 h octahedral site increases and that occupying the 24d tetrahedral site decreases.