The corresponding VT spectra of the lower V-substituted, pseudo-cubic phase Bi 0.913 V 0.087 O 1.587 , however, show evidence for only one type of V environment centred at -478 ppm (Figure , left) with a much broader CT linewidth at room temperature and no observed ST spinning sideband intensity, consistent with a distribution of similar VO 4 polyhedra. Upon heating, the CT linewidth narrows markedly, accompanied by the appearance and then linewidth narrowing of spinning sidebands; interestingly, this corresponds to the higher-temperature behaviour of the V sites in the highly V-substituted sample (Bi 0.852 V 0.148 O 1.648 ). As with Bi 0.852 V 0.148 O 1.648 , a similar shift change to lower frequency (-458 ppm) occurs, corresponding to an average increase in V coordination. We can conclude that the motion probed by the single V environment, even at room temperature, is already of a similar rate to the MAS spinning frequency (4 kHz) and therefore much faster than that experienced by the equivalent sites in Bi 0.852 V 0.148 O 1.648 . Additionally, there is no evidence of additional V environments as in the lower V-substituted Bi 0.913 V 0.087 O 1.587 . These results from V NMR are in good agreement with the 17 O NMR data, in which at moderate temperatures up to coalescence, only one average feature in the V-O region is observed for Bi 0.913 V 0.087 O 1.587 , but two such peaks are present for Bi 0.852 V 0.148 O 1.648 .