Investigations into the fast ionic conductors γ-CuBr, Li2S, Na2S, Ba2NH, NaTaN2 and Li3HoCl6 by means of neutron scattering

The main topic of this work was the investigation of ionic diffusion in solids by means of neutron scattering. Experiments were carried out on the antifluorites Li2S, Na2S and γ-CuBr (zinc-blende type) as well as on Barium-Nitride-Hydride Ba2NH, NaTaN2 and Li3HoCl6 which represent three-and two-dimensional ionic conductors, respectively. In the sulphur based antifluorites Li2S and Na2S the occupation of the interstitial empty cube site by cations occurs at elevated temperatures. The temperature-dependence of the diffusion process has been investigated by quasielastic, incoherent neutron scattering. The cations hop between their regular lattice sites and the interstitial empty cube site, whereas the sulphur ions vibrate in good approximation harmonically even at high temperatures. The jump vectors define a three-dimensional net of possible cation paths through the crystal. The analysis of quasielastic scattering experiments on a Li2S single crystal enabled us to determine the jump vectors and the jump rates 1/τ. The temperature dependence of the anharmonic contributions to the copper structure factor was the main point in our neutron diffraction experiments on γ-CuBr. It could be shown that the copper density function deviates strongly from the isotropic form with increasing temperature. Barium-Nitride-Hydride is one of the few documented H--ionic conductors. The electronic part of the ds-conductivity is only 1/10000 of the ionic contribution. Since Ba2NH is a layer compound, where H- and N3- layers alternate along the c-axis, the probability of jumps out of the plane is suppressed in favour of in plane jumps. This compound is therefore a model system in which two-dimensional diffusion can be studied and in fact the analysis of the quasielastic data proved that the H-diffusion is caused by jumps between regular H- lattice sites. (author) figs., tabs., refs