For the more highly V-substituted, monoclinic Bi 0.852 V 0.148 O ) indicate conduction processes that differ from the sublattice exchange evident from the two-site coalescence observed for the Vsubstituted samples. Focussing on the O Bi region of the spectra, three distinct regimes are active at different temperatures. From room temperature to 473 K, only one broad O Bi resonance is observed, consistent with slow ionic motion and/or a large chemical shift distribution that prevents the resolution of individual sites. From 523-673 K two distinct environments at ∼220 and ∼200 ppm are resolved, which are tentatively ascribed to O near, and not near, an oxide ion vacancy in the Bi-O sublattice; this assignment is consistent with the oxygen vacancies observed in this phase previously. (We note a two-peak fit is justified as second-order quadrupolar coupling lineshapes are not expected, with further details given in the SI.) At these temperatures, the higher-frequency resonance at ∼220 ppm displays a narrowing linewidth with increasing temperature. We attribute this behaviour to the vacancy-adjacent oxygen atoms undergoing hopping into vacancy sites. By contrast, the isolated oxygens in fully occupied regions of the lattice are immobile, and therefore the corresponding spectral feature (at ∼200 ppm) exhibits an invariant linewidth with increasing temperature. (Two O Bi resonances at ∼220 ppm and ∼200 ppm are also observed in the O spectra of both V-substituted samples, especially in the spectra collected at 573 K, showing that O sites adjacent to vacancies can be distinguished in all the studied phases.)