Regensburg 2007 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 10: Dielectric and Ferroelectric Thin Films and Nanostructures III
DF 10.10: Vortrag
Donnerstag, 29. März 2007, 17:30–17:50, H48
Ab initio study of the critical thickness for ferroelectricity in ultrathin lead titanate films between conducting electrodes — •Christian Elsässer1,4, Yoshitaka Umeno2, Bernd Meyer3, and Peter Gumbsch4,1 — 1Fraunhofer-Institut für Werkstoffmechanik, Freiburg — 2Graduate School of Engineering, Kyoto University, Japan — 3Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum — 4Institut für Zuverlässigkeit von Bauteilen und Systemen, Universität Karlsruhe
The ferroelectricity of single-domain ultrathin PbTiO3 films sandwiched between metallic Pt electrodes has been studied using ab-initio density-functional theory (DFT) calculations within the local-density approximation [1]. For stress-free PbTiO3 films with an in-plane lattice constant of the tetragonal bulk phase we find that the films lose ferroelectricity below a critical thickness of about 4 and 6 unit cells (1.6 nm and 2.4 nm) for PbO- and TiO2-terminated films, respectively. This result is in contradiction to a recent DFT study by Sai, Kolpak and Rappe [2], in which the persistence of ferroelectricity for Pt/PbTiO3/Pt films down to one unit cell (0.4 nm) has been reported. Careful tests with different types of pseudopotentials and density-functionals reveal that this discrepancy is due to insufficiencies of the widely used generalized-gradient approximations PW91 and PBE, which have been employed by Sai et al. for describing perovskite compounds. [1] Y. Umeno, B. Meyer, C. Elsässer, P. Gumbsch, Phys. Rev. B 74, 060101(R) (2006). [2] N. Sai, A. M. Kolpak, A. M. Rappe, Phys. Rev. B 72, 020101(R) (2005).