Deep hydration of an Li7-3xLa3Zr2M IIIxO12solid-state electrolyte material: A case study on Al- and Ga-stabilized LLZO

Abstract

Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li7La3Zr2O12(LLZO), have been analysed using single-crystal X-ray diffraction to determine the pristine structural state immediately after synthesis via ceramic sintering techniques. Hydrothermal treatment at 150°C for 28 d induces a phase transition in the Al-stabilized compound from the commonly observed cubic Ia d structure to the acentric I 3d subtype. LiIions at the interstitial octahedrally (4+2-fold) coordinated 48e site are most easily extracted and AlIIIions order onto the tetrahedral 12a site. Deep hydration induces a distinct depletion of LiIat this site, while the second tetrahedral site, 12b, suffers only minor LiIloss. Charge balance is maintained by the incorporation of HI, which is bonded to an O atom. Hydration of Ga-stabilized LLZO induces similar effects, with complete depletion of LiIat the 48e site. The LiI/HIexchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.