Motional narrowing under diffusion of two spin sub-lattices in LiNaSO4

An expression for the dipolar correlation function characterizing the fluctuations of the Hamiltonian under uncorrelated diffusion of two cationic sub-lattices in a solid has been obtained. A corresponding formula, which can be used for fitting the two-step temperature dependencies of the NMR line width, has been deduced. We also considered the case of a distribution of correlation times and deduced a corresponding analytical fitting function. Elaborated expressions have been applied to the NMR line width analysis of LiNaSO4 in the temperature range 295–788K. [Display omitted]