It was recalled that ion-conducting rotor phases were high-temperature modifications of simple inorganic salts, typically with a cubic structure. Therein, polyatomic tetrahedral anions such as SO42- and PO43- exhibited considerable rotational disorder while the cations exhibited fast ion conductivity. It remained unclear whether anion reorientational motion affected or enhanced cation transport in these materials. A study was made of quasi-elastic neutron scattering from the ion-conducting rotor phases, LiNaSO4, Na3PO4 and Li2SO4. The diffusion of Na ions in Na3PO4 was examined by means of back-scattering spectrometry. The data could be easily explained in terms of the Chudley-Elliott model; thus yielding reasonable values for the jump distances, mean residence times and diffusion coefficients. In Na3PO4, the linewidths due to anion reorientation and cation hopping differed by some 3 orders of magnitude. The situation in Li2SO4 and LiNaSO4 was completely different. Here, both types of motion had a similar timescale, and time-of-flight experiments revealed both diffusional and reorientational contributions to quasielastic scattering.

Ion Conducting Rotor Phases - New Insights from Quasielastic Neutron Scattering. D.Wilmer, H.Feldmann, J.Combet, R.E.Lechner: Physica B, 2001, 301[1-2], 99-104