An ideal garnet has the formula; A3B2X3O12, where A, B and X are eight, six and four coordinated cation sites, respectively, which crystallise in a face-centred cubic structure (e.g. A = Mg, Fe, B = Al, Cr, Fe, and X = Si, Fe, Al, Ga) . This structure comprises BO6 octahedra and XO4 tetrahedra, arranged in a 3D framework wherein larger A cations occupy dodecahedral positions in the interstices . Lithium ions fully occupy the tetrahedra 24d site, with 3 Li per formula unit (pfu). Alteration of A and B sites dopants, such as in La3Zr2Li7O12 (LLZO), enables up to 7 Li pfu (the upper maximum). However, at this point the system changes from a highly conductive cubic phase (Ia3 ̅ d or I43 ̅ d, Li content ~6.2-6.55 pfu), with vacant interstitial sites for ionic mobility, to a system whereby Li sites are fully occupied and have thus ordered (to reduce short Li-Li distances) . This gives a reduction in symmetry from a cubic to a tetragonal cell (I41/acd) with ordered lithium occupying the tetrahedral (8a) and distorted octahedral (16f/32g) sites .