Microstructure and properties investigation of garnet structured Li7La3Zr2O12 as electrolyte for all-solid-state batteries

Garnet structured Li7La3Zr2O12 is investigated in its pure, tetragonal phase and its stabilized cubic phase by substitution with different amounts of Ta and Al. The effect of substitution and sintering conditions on phase composition, microstructure, electrical properties and, as main focus, the mechanical properties are investigated. Sintering is carried out in air and argon atmosphere at temperatures of 1150 and 1200 °C. The Ta substitution ranges up to 60% and the Al substitution up to 36% to obtain fully cubic samples. The mechanical properties were assessed via depth-sensitive indentation testing and interpreted in terms of properties of the material and effective properties of the porous specimens. Complementary, ab initio calculations were performed to determine the structural and mechanical properties. The study verifies the strong dependency of the ionic conductivity on substitution, phase composition and materials density. Overall, the effect of substitution and phase composition can be mostly seen in changes in the intrinsic materials properties, whereas the effects of sintering conditions and porosity can mostly be seen in the change in effective mechanical properties.