Effects of alkaline earth metal doping on garnet Li7La3Zr2O3

•The effects of alkaline earth metal (Ca, Sr, Ba) doping on garnet LLZO were investigated.•Successful substitution of alkaline earth metals into the La site of LLZO was achieved.•Alkaline earth metal doping did not show a significant effect on Li-distribution.•Ba doping led to lower resistance at grain boundary and enhanced ionic conductivity.•The highest ionic conductivity was obtained with Ba doping due to its largest ionic radius among the doped elements. The garnet Li7La3Zr2O12(LLZO) has gained significant attention as a promising solid electrolytes for all-solid-state Li-ion batteries. However, the cubic phase of LLZO, which offers better ionic conductivity compared to the tetragonal phase, is thermodynamically unstable under ambient conditions. We synthesized and investigated ternary-doped LLZO to stabilize the cubic phase and enhance its ionic conductivity. The effects of doping on the crystal structure, microstructure, and ionic conductivity were characterized by various measurement techniques. The results reveal successful incorporation of the ternary-doped elements into the cubic garnet structure without formation of secondary phases. Specifically, the introduction of alkaline earth metals with increased ionic radius resulted in an expansion of the crystal lattice and enhanced microstructure. These beneficial effects of doping led to the highest ionic conductivity of 4.29 × 10-4S cm−1 for Li6.45Ga0.133La2.95Ba0.05Zr1.8Ta0.2O12with a relative density of 94.63%.