Hydrothermally treated Al- and Ga-stabilized stuffed Li garnets, nominally Li 7La 3Zr 2O 12, have been investigated by single-crystal X-ray diffraction to determine structural and site-occupation alterations due to Li I/H I exchange.
Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li 7La 3Zr 2O 12 (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 3 d subtype. Li I ions at the interstitial octahedrally (4 + 2-fold) coordinated 48 e site are most easily extracted and Al III ions order onto the tetrahedral 12 a site. Deep hydration induces a distinct depletion of Li I at this site, while the second tetrahedral site, 12 b, suffers only minor Li I loss. Charge balance is maintained by the incorporation of H I, which is bonded to an O atom. Hydration of Ga-stabilized LLZO induces similar effects, with complete depletion of Li I at the 48 e site. The Li I/H I exchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.