Identification of the Li sites in the Li ion conductor, Li6SrLa2Nb2O12, through neutron powder diffraction studies

In this paper a neutron powder diffraction structural study of the Li ion conducting garnet-related system, Li6SrLa2Nb2O12, is reported. The results show that this phase is cubic, space group I a - 3 d , and contains Li in two partially occupied crystallographic sites. The first site, Li1, corresponds to the ideal tetrahedral site in the garnet framework and possesses an occupancy of 0.59(1). The second site, Li2, is significantly more distorted and possesses an occupancy of 0.352(3). Compared to the related Li5La3Nb2O12 system, the Li2 site occupancy is greatly increased, while the Li1 site occupancy is reduced. Despite these large differences in site occupancies, the reported conductivities for Li5La3Nb2O12 and Li6SrLa2Nb2O12 are similar, showing the complexities of these new garnet Li ion conductors.