Regensburg 2007 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 11: Poster Session
DF 11.3: Poster
Donnerstag, 29. März 2007, 14:30–18:00, Poster C
Size and Doping Effects of Ferroelectric Nanoparticles: A Microscopic Model — Thomas Michael1, •Julia Wesselinowa2, and Steffen Trimper1 — 1Institute of Physics, Martin-Luther-University Halle, D-06099 Halle Germany — 2University of Sofia, Department of Physics, Blvd. J. Bouchier 5, 1164 Sofia, Bulgaria
A microscopic model for describing ferroelectric nanoparticles is proposed. It enables the calculation of the macroscopic polarization as a function of an external electric field, the temperature, the defect concentration and the particle size. Furthermore the excitation energy of the soft mode and its damping can be computed. The constituents of the material are arranged in layers. Their interaction depends on both the coupling strength at the surface and that of defect shells in addition to the bulk values. The analysis is based on an Ising model in a transverse field. It is modified in such a manner to study the influence of size and doping effects on the hysteresis loop of spherical nanoparticles. Using a Green’s function technique in real space we find the coercive field, the remanent polarization and the critical temperature which differ significantly from the bulk behavior. Depending on the kind of doping ions and the surface configuration the coupling strength varies. Hence the coercive field and the remanent polarization can either increase or decrease in comparison to the bulk behavior. Theoretical results are compared with experimental data.