Regensburg 2002 – wissenschaftliches Programm
DY 46.33: Poster
Donnerstag, 14. März 2002, 15:30–18:00, D
Temperature Dependence of the Lattice Dynamics of the Ionic Conductors CaF2 and LaF3 — •Karin Schmalzl1, Dieter Strauch1, Franz Demmel2, Bruno Dorner2, Oliver Lips3, and Mohammed Saad3 — 1Institut für Theoretische Physik, Universität Regensburg, 93053 Regensburg, Germany — 2Institut Laue-Langevin, 38042 Grenoble Cedex 9, France — 3Institut für Festkörperphysik, TU Darmstadt, 64289 Darmstadt, Germany
The fluoride crystals CaF2 and LaF3 are superionic
conductors with a strong increase of fast ionic conductivity at
1430 K and 1150 K, respectively.
We compare the structural and dynamical properties determined with the help of ab initio calculations with results from inelastic neutron scattering experiments.
Single crystal (TAS) inelastic neutron scattering studies have been carried out to investigate the temperature dependence of the lattice dynamics of these systems. We observed an anomalous softening of one phonon mode in CaF2 which is attributed to oscillations in the fluorine sublattice. In contrast, for LaF3 we have detected a shift to higher frequencies for one mode with increasing temperature.
Calculated frequencies reasonably agree with experimental data.
The anion conductivity in CaF2 will be calculated by means of ab-initio molecular dynamic simulations at a final temperature. In a first step defect structures will be studied.