Above 573 K, both resonances disappear for both samples, before reappearing as a single coalesced resonance at 823 K; the shift of this coalesced feature is 332 ppm for Bi 0.913 V 0.087 O 1.587 and 391 ppm for Bi 0.852 V 0.148 O 1.648 . This behaviour is indicative of exchange between the two proaches the frequency separation between the two spectral features. Interpolation using the full set of spectra (see SI) allows us to estimate the temperature at which the maximum broadening and initial coalescence is observed, where the rate of ionic motion is directly proportional to the frequency separation. On this basis, we calculate sublattice exchange rates of 87 kHz at 723 K for pseudo-cubic Bi 0.913 V 0.087 O 1.587 , and 86 kHz at 748 K for monoclinic Bi 0.852 V 0.148 O 1.648 . At comparable temperatures, the motional rate is somewhat slower in the more highly V-substituted, crystallographically lower-symmetry material.