High-temperature structural phase transitions in pure and Al, Ga and Fe substituted Li7La3Zr2O12 garnet-type solide state electrolyte materi

Substituted Li7La3Zr2O12 (LLZO) is a highly prospective material for application as a solid electrolyte in solid-state batteries due its high Li-ion conductivity. With Al3+ a cubic Ia-3d garnet structure is stabilized, small amounts of Ga3+ or Fe3+ stabilize an I-43d structure. Ga-LLZO and Fe-LLZO show phase transitions between 280–350°C in fresh and aged material. The existence and the nature of these phase transitions has not been reported in literature of LLZO so far (hardy to observe with powder data) and we propose to investigate it in detail using single-crystalline material in an in-situ high-temperature synchrotron-diffraction study. Pure LLZO is tetragonal and transforms to the Ia-3d structure at Tc ~ 645°C, in aged material a more complex transformation series is reported, which also needs a more detailed study to explain its nature. Also, for pure LLZO, no detailed structural information on phase transition behaviour is available for this technological relevant material.