Phase transformation of the garnet structured lithium ion conductor: Li7La3Zr2O12

Abstract Phase stability of the Garnet-structured lithium ion conductor Li 7 La 3 Zr 2 O 12 (LLZ) was investigated using high-temperature X-ray diffraction (HT-XRD). The tetragonal LLZ containing CO 2 transformed to the cubic phase around 150 °C. However, once the tetragonal LLZ heated up to 1000 °C, the cubic phase transformed back to the tetragonal phase again, because of the CO 2 loss during the heating process. After the CO 2 loss, the phase transformation temperature shifted to 650 °C. The HT-XRD study for Al-doping process was also performed. The addition of γ-Al 2 O 3 to the tetragonal LLZ eliminated the formation of impurity phase such as La 2 Zr 2 O 7 and La 2 O 3 , resulting in the formation of a pure cubic phase. A comparison of the HT-XRD results suggested that the Li loss is necessary to stabilize the cubic phase with Al.