Unresolved correlation time spectra and interpretation of NMR relaxation time data for superionic conductors

Problems in relating the results of NMR relaxation time measurements to the results of bulk conductivity/diffusion studies for superionics have been discussed in a number of ways, such as their being a result of lack of knowledge of the appropriate motional correlation function. It is argued that, in the case of hydrated proton conductors at least, the problem is more fundamental. When previously unrecognized temperature-dependent correlation time spectra are present, these cannot be resolved in reduction of relaxation time data and information on any single contributory motion is not simply available.