DFT Study of the Role of Al(3+) in the Fast Ion-Conductor Li(7–3x)Al(3+)(x)La(3)Zr(2)O(12) Garnet

[Image: see text] We investigate theoretically the site occupancy of Al(3+) in the fast-ion-conducting cubic-garnet Li(7–3x)Al(3+)(x)La(3)Zr(2)O(12) (Ia-3d) using density functional theory. By comparing calculated and measured (27)Al NMR chemical shifts an analysis shows that Al(3+) prefers the tetrahedrally coordinated 24d site and a distorted 4-fold coordinated 96h site. The site energies for Al(3+) ions, which are slightly displaced from the exact crystallographic sites (i.e., 24d and 96h), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad (27)Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al(3+) could also occupy the 48g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al(3+) site has not been observed experimentally.