Therefore, B site substitutions would have a greater chance of changing any structure-based transition temperature. This is supported by the results for LaSr2B2Li7O12 (B = Nb, Ta) and La3Sn2Li7O12 (tetragonality 0.956, transition temperature 750-800°C ) whereby large differences in tetragonality (compared to A site substitutions) correspond to higher transition temperatures. Hence, the cell volume alone is not the ideal measure of transition temperature, rather the key numerical indicator could be considered the tetragonality which effectively mimics the thermodynamic energy barrier to overcome when transitioning from Li order to disorder. Hence this suggests the degree of tetragonality is a more important indicator for the cell transition temperature, and that this is controlled more by the B site composition, as A site substituents have much reduced lattice parameters yet the degree of tetragonality remains similar, as do the transition temperatures. As such, attempts to increase Ce content beyond the 0.25 reported by Dong et al. were made, via employing dry room facilities. However, this led to Ce based impurities (see figure ), in addition to tetragonal LLZO, similar to the reports in the work . As employing larger 4+ ions than Ce is not feasible, co-doping strategies (such as Y/Nb or Sc/Nb) need to be considered to reach the octahedral radius of 0.76 Å. For example, a garnet with formula of La3YNbLi7O12 yields an average octahedral site radius of 0.77 Å 72 . This was attempted via the standard solid state route. While, this did indeed yield a cubic phase, large Nb, Y and La oxide-based impurities were present, see figure .