In the first reported synthesis Murugan et al. made use of a conventional solid-state method with LiOH, La 2 O 3 , and ZrO 2 with a sintering temperature of 1230 • C. Unfortunately, such a high sintering temperature results in substantial Li loss and can furthermore lead to destabilisation of the LLZO structure and formation of the competing pyrochlore: La 2 Zr 2 O 7 . Undoped materials prepared by sol-gel synthesis has been shown to have approximately 3 times higher conductivity than solid-state prepared, most likely due to more homogenous and dense samples. However, LLZO prepared by the sol-gel method show lower thermal stability, due to larger grain size. A further alternative is to use pulsed laser deposition (PLD) allowing for precise control of composition and stoichiometry, and can be used to prepare thin films of LLZO. One of the challenges concerning LLZO is the relatively poor ionic conductivity at grain boundaries, the reasons for which are debated. In general, grain boundaries in oxide electrolytes are known to reduce the overall ionic conductivity, although the opposite can also be true for some materials. As a result, the sintering process of the electrolyte is important for reducing the grain boundary to bulk ratio. Grain boundaries in LLZO have also shown a susceptibility to Li dendrite formation and propagation. Additionally, good electrode-electrolyte contact is difficult to achieve, and easily forms cracks, leading to poor ionic conductivities as well as dendrite growth. The main difference between the cubic and the tetragonal LLZO structure is the Li sublattice. In the tetragonal structure there are three fully occupied Li Wyckoff sites; Li 8a , Li 16f , Li 32g , a tetrahedral, an octahedral and a distorted octahedral site, respectively. In the cubic structure there are only two different Wyckoff sites; Li 24d , Li 96h , a tetrahedral and a distorted octahedral site. Both sites are partially occupied and thus the Li sublattice in the cubic structure is often described as disordered. Furthermore, a third Wyckoff site, Li 48g , is also often mentioned, but is an average position of a pair of Li 96h sites. The tetragonal and the cubic structure are visualised together with their Li Wyckoff sites in Figure and SI Figure , respectively.