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

Abstract

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.

Thermodynamic properties andp-Tphase diagrams of (NH4)3M3+F6cryolites (M3+: Ga, Sc)

“…However only PTs at T 1 and T 2 can be considered as associated with the ordering process according to the values of entropy close to R ln 8 and to R ln 2, respectively. This supposition is proved by the NMR results for (NH 4 ) 3 InF 6 [18] which also seemed, based on the data [7,19], to undergo a succession of three PTs. The anomalous temperature behaviour of the spin-lattice relaxation times T 1H and T 1F were detected only at T 1 and T 2 .…”

“…This value is in good agreement with entropies found experimentally in [5,7] and in the present paper for ammonium cryolites with M 3+ : Ga, V, Fe. The model of PT F m 3m-P 1 as connected with simultaneous ordering of octahedra and tetrahedra was proved by the results of the NMR studies of the Ga compound [18] where the discontinuity in the spin-lattice relaxation time for the proton and fluorine nucleus was detected at PT point.…”