The Li 24d site preference of Al in LLZO is well documented and is also reported for Ga. However, NMR studies found both Al and Ga ions to be equally distributed over the 24d and 96h sites. NMR spectroscopy studies also indicate that Al substitutes both Zr and La sites at high doping concentrations. Experiments with co-doping with both Al and Ga have been shown to stabilise the cubic phase and increase the ionic conductivity with Ga often reported to give higher ionic conductivities, however the reason for this is not well understood. In garnet materials, other phases with relatively low melting temperatures, such as LiAlO 2 , Li 5 AlO 4 , and LiGaO 2 , are often reported in the grain boundaries and are believed to aid grain growth and densification during sintering. Nb and Ta have also been shown to stabilise the cubic LLZO structure, both preferring Zr sites, thus acting as donor dopants and increasing the V ′ Li concentration.