The O P environment in Bi 0.852 P 0.148 O 1.648 appears to have a short, temperature-invariant T 1 value of ∼1 ms, as shown in the SI, although signal from this site could not be deconvoluted at several temperatures in the O relaxation measurements due to overlap with the O Bi resonance. 1 values and the features have been analysed together. In the case of Bi 0.852 P 0.148 O 1.648 , T 1 values for the O P environment were consistently too short to reliably measure (< 1 ms) and/or the O P features were not resolved at certain temperatures due to overlap with the O Bi resonance.