Fig. 3: Sodium site occupancies as a function of Na content.

Panel (a) shows the average Na site occupancy at the Na(1) site (blue circles) and the Na(2) site (blue triangles) from the kMC simulations at 443 K; they are compared with previous Grand Canonical Monte Carlo simulations19 (red circles and triangles) at the same temperature, and existing experimental data30 (in orange circle and triangles). Dashed lines are used as guide for the eye. Panel b shows \({{{{{{{\rm{N}}}}}}}}({{{{\rm{N}}}}}{{{{{\rm{a}}}}}}^{{{{{\rm{+}}}}}})\times {{{{{{{\rm{N}}}}}}}}\left({{{{\rm{Vacancy}}}}}\right)\) (solid blue curve, per f.u.) at 443 K from kMC simulations. The contributions to \({{{{{{{\rm{N}}}}}}}}({{{{\rm{N}}}}}{{{{{\rm{a}}}}}}^{{{{{\rm{+}}}}}})\times {{{{{{{\rm{N}}}}}}}}\left({{{{\rm{Vacancy}}}}}\right)\) from individual sodium sites, Na(1) and Na(2) are shown as blue dashed lines. In panel (b), the shaded regions mark areas where Na-ion conductivity is highly (red) or slightly (blue) impacted by the charge carrier concentration.