Reorientation of tetramethylammonium ions in TMMC studied by incoherent quasielastic neutron scattering (IQNS)

INS experiments were performed at the Institut Laue-Langevin (Grenoble, France) on crystals with formula (CH3)4NMnCl4 (TMMC) in order to analyze the reorientations of the tetramethylammonium cations (TMA) in the dynamically disordered phase of the crystal. From the analysis of the elastic incoherent structure factors (EISF), extracted from the data recorded on a very large scale of instrumental resolutions, we were able to propose a model of jumps of TMA over 20 sites distributed among three semicircular arcs joining together on a threefold C3 axis. Then, a preliminary quantitative description of the motions involved in the high temperature phase is proposed. (orig.)