New Technique for Determining the Diffusion Mechanism by NMR: Application toCl35Diffusion in TlCl

A major problem in the study of atomic motions is the determination of the dominant mechanism responsible for translational diffusion. Recently Ailion and Ho predicted that the rotating-frame spin-lattice relaxation time $T_{1\rho }$ would have an angular dependence which depends on the diffusion mechanism in the ultraslow-motion region. In this paper we have extended these ideas to TlCl for which the dominant mechanism is known by other experiments to be Cl vacancy diffusion. We observed experimentally an angular dependence consistent with the dominant mechanism being Cl vacancy diffusion, thereby corroborating the basic ideas of Ailion and Ho. We have also been able to eliminate Cl interstitialcy diffusion as a possible dominant mechanism. We measured an activation energy of (0. 733 ± 0. 012) eV, in agreement with results of other experiments.