Ionic reorientations and phase transition in solid IF6AsF6

Abstract

19F static and rotating frame spin–lattice relaxation times (T1 and T1ρ) as well as broadline NMR studies have been carried out on solid IF6AsF6 between 213 and 393 K. From the T1– and T1ρ–temperature behaviour, we inferred a phase transition at 350(± 2) K and a supercooled high temperature phase. In both phases the second moments are consistent with a model where both IF6+ and AsF6− reorient about random axes. The T1 and T1ρ data in the low temperature phase can be interpreted in terms of a single frequency factor τ0 = 3.15(± 0.2) × 10−16 s and activation energy Ea = 10.4(± 0.4) kcal/mol for both cation and anion reorientation. At the temperature of the phase transition the ionic-reorientational frequencies become faster by ~ 2 orders of magnitude. In the high temperature phase T1 and T1ρ are essentially independent of temperature which may be associated with a spin–rotation relaxation mechanism.