Deep hydration of an Li(7–3x )La(3)Zr(2) M (III) ( x )O(12) solid-state electrolyte material: a case study on Al- and Ga-stabilized LLZO

Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li(7)La(3)Zr(2)O(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 [Image: see text] d structure to the acentric I [Image: see text] 3d subtype. Li(I) ions at the inter­stitial octa­hedrally (4 + 2-fold) coordinated 48e site are most easily extracted and Al(III) ions order onto the tetra­hedral 12a site. Deep hydration induces a distinct depletion of Li(I) at this site, while the second tetra­hedral site, 12b, 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 48e 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.