Reorientational Motions and Self‐Diffusion of Ions in (NH4)3[InF6] and (NH4)3[GaF6] Crystals as Studied by 1H and 19F Nuclear Magnetic Resonance and Electrical Conductivity Experiments

The spin-lattice relaxation time T1 and the NMR second moment M2 of 1H and 19F nuclei were determined at various temperatures above 77 K for (NH4)3[InF6] and (NH4)3[GaF6] crystals. From the fact that small M2 values observed for both nuclei from fairly low temperatures, it is concluded that the reorientational motions of NH4+ cations and complex anions are activated even below and near room temperatures, respectively, in addition to the onset of translational self-diffusion of the cations at higher temperatures. The motional parameters of both cations and complex anions in (NH4)3[InF6] crystals were estimated from the analysis of the temperature dependence of T1 observed for both nuclei. The occurrence of ionic self-diffusion was confirmed by electrical conductivity measurements and the activation energy for the motion was evaluated as 38 and 37–41 kJ mol−1 for the high temperature cubic phase of (NH4)3[InF6] and (NH4)3[GaF6], respectively.