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DY: Dynamik und Statistische Physik

DY 46: Poster

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.