Measurement of the spin-lattice (T 1 ) relaxation times as a function of temperature can be used to gain insight into ionic motion correlation rates on the order of the Larmor frequency (∼ 10 8 Hz), a motional regime well above that accessible through CT linewidth measurements, which are only sensitive to motion on the order of the MAS rate (∼10 4 -10 5 Hz). By measuring the O T 1 values for both the O Bi and O V sites as a function of temperature, the relative contributions to ionic motion in these materials can be determined. Results from O T 1 measurements for Bi 0.913 V 0.087 O 1.587 , Bi 0.852 V 0.148 O 1.648 and Bi 0.852 P 0.148 O 1.648 are shown in Figure .