Deep hydration of an Li7-3xLa3Zr2MIIIxO12solid-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\overline{3}d structure to the acentric I\overline{4}3d subtype. LiI ions at the inter­stitial octa­hedrally (4 + 2-fold) coordinated 48e site are most easily extracted and AlIII ions order onto the tetra­hedral 12a site. Deep hydration induces a distinct depletion of LiI at this site, while the second tetra­hedral site, 12b, suffers only minor LiI loss. 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 LiI at the 48e site. The LiI/HI exchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.