In ref. , a similar study was performed for the same substitution series. In this case, bond valence calculations, also based on structural models obtained from neutron diffraction alone, show some difference in the activation energies for both diffusion pathways (0.483 eV and 0.456 eV for paths along the ab-plane, and 0.509 eV along the c-direction). Therefore, it was suggested that though 3D diffusion is possible, the diffusion is likely faster in the ab-plane and therefore anisotropic, however no experimental data on short-range ion transport was presented.