Plenarvorträge - DPG-Tagungen

Dielektrische Festkörper Mittwoch
DF 5.13 Mi 14:30 Poster C
Molecular dynamics studies of the thermodynamic and structural
temperature behaviour of Li2B4O7 — •Volodymyr V.
Maslyuk 1 and Herbert Pfnür 2 — 1 Uzhhorod National University,
Ukraine — 2 Institut Für Festkörperphysik, Universität Hannover, Germany
By ab initio calculation we show that B atoms in triangular BO3 and
tetragedral BO4 configurations are non equivalent. Whereas B in BO3
carries a one charge, it is another charged in BO4, will corresponding consequences
on the lateral interactions with the oxygen atoms. We generate
effective potentials that gives a good description of the (1−x)Li2OxB2O3
system. Molecular dynamics calculation carried out will this effective description
allows to determinate the temperature behaviour of lattice parameters,
angles between atoms and the heat capacity of Li2B4O7. An
abnormal behaviour of lattice parameter c was found that is in excellent
agreement with experimental data [1].
[1] V. V. Zaretski and Ya. V. Burak, Physics of the Solid State, 31, 6,
960-963, 1989
DF 5.14 Mi 14:30 Poster C
Orientation-dependent ELNES of TiO2: a comparison of
theory and experiment — •Christian Heiliger 1,2 , Frank
Heyroth 1 , Frank Syrowatka 1 , Wolfram Hergert 2 , and
Ingrid Mertig 2 — 1 Center of Materials Science, Martin-Luther-
University Halle-Wittenberg, Hoher Weg 8, 06120 Halle, Germany —
2 Martin-Luther-University Halle-Wittenberg, Department of Physics,
Von-Seckendorff-Platz 1, 06120 Halle, Germany
In this poster we present a spectroscopic investigation of titanium oxid
(TiO2). The usage of the ultra high vacuum STEM (scanning transmission
electron microscope) VG HB 501 equipped with a Gatan Enfina
PEELS detector gives the opportunity to detect EELS (electron energy
loss spectra) with a high energy resolution. For that reason one can observe
characteristic differences in the spectra between the 3 phases of
TiO2: rutile, anatase and brookite. In addition it is possible to investigate
the orientation dependence of the samples.
Apart from the experimental discussion a comparison to theoretical
calculations is presented. The calculation is based on the DFT (density
functional theory) within the LDA (local density approximation) using
the Stuttgart-LMTO-47 (linearized muffin tin orbitals) package. Taking
into account the core hole effect in the Z+1 or Z+2 approximation a very
good agreement in the peak positions is observed. The peak intensities
however are not correctly reflected.
DF 5.15 Mi 14:30 Poster C
The structure of plain and stepped BaTiO3 surfaces — •Walter
Alsheimer, Sibylle Gemming, and Gotthard Seifert — Institut
für Physikalische Chemie und Elektrochemie, TU Dresden, D-01062 Dresden
In the framework of miniaturization of semiconductor devices ferroelectric
compounds in the perovskite structure attract much interest. For
example one of our aims is to deliver a density-functional based understanding
of an organic field effect transistor on a ferroelectric template
like BaTiO3.
Because of the low computational costs the density-functional based
tight binding (DFTB) method allows one to study complex and large
structures. Therefore in a first step we choosed this technique to perform
calculations on the relaxation of plain and stepped surfaces with a
slab model geometry. Trends for the interplanar spacings and the local
coordination at the step edge are discussed for vicinal (10n) surfaces.
DF 6 Nanostrukturen, Schichten und Keramiken
Zeit: Donnerstag 09:30–12:30 Raum: H11
Hauptvortrag DF 6.1 Do 09:30 H11
Probing ferroelectricity at small length and short time scales
— •Theo Rasing — NSRIM Institute, University of Nijmegen, Toernooiveld
1, NL-6525 ED Nijmegen, The Netherlands
Future applications of ferroelectric materials in nanoelectronic or storage
devices require the control and manipulations/switching of ferroelectricity
on small (submicron) length scales and short (subnanosecond)
time scales. These developments in turn ask for methods to probe ferroelectric
properties at these length and time scales as well.
Our recent progress report in this area will be discussed, demonstrating
in particular the use of scanning probe and nonlinear optical methods to
investigate the static and dynamic properties of ferroelectrics with a lateral
resolution down to the nanometer regime (using a scanning probe)
and a time resolution down to the picosecond regime (using nonlinear
optical microscopy). Finally, the possibility to combine the best of both
worlds, namely the time resolution offered by femto-second lasers with
the lateral resolution of scanning probe methods will be demonstrated.
Hauptvortrag DF 6.2 Do 10:10 H11
Charakterisierung von PZT-Keramiken mit hochauflösender
Röntgenspektroskopie — •M. J. Hoffmann — Institut für Keramik
im Maschinenbau, Zentrallaboratorium der Universität Karlsruhe,
Haid-und-Neu-Str.7, 76131 Karlsruhe
Keramiken auf der Basis von Bleizirkonattitanat (PZT) haben, aufgrund
ihrer herausragenden piezoelektrischen Eigenschaften, eine große
technische Bedeutung im Bereich der Sensorik und Aktorik. Die di- und
piezoelektrischen Eigenschaften erreichen ihre Maximalwerte bei Zusammensetzungen
in der Nähe der morphotropen Phasengrenze (MPB), die
durch die Koexistenz einer ferroelektrisch tetragonalen und einer ferroelektrisch
rhomboedrischen Phase charakterisiert ist. Im Rahmen des
Vortrags wird zunächst die Wechselwirkung beider Phasen im Gefüge
anhand der oberflächensensitiven Röntgenspektroskopie diskutiert. Es
werden mögliche Phasenumwandlungen bis zur Curie-Temperatur und
deren Einfluss auf die Materialeigenschaften diskutiert. Im zweiten Teil
des Vortrags werden hochauflösende Synchrotronmessungen vorgestellt,
mit denen der extrinsische (Domänenschaltprozesse) und intrinische (Piezoeffekt)
Beitrag zur Gesamtdehnung einer PZT-Keramik quantifiziert
werden kann. Es wird gezeigt, dass die höchste piezoelektrische Dehnung
nicht der Richtung der spontanen Polarisation entspricht. Anschließend
werden die Unterschiede in der Beweglichkeit von nicht-180 0 Domänen
für beide ferroelektrische Phasen diskutiert. Aus einem Vergleich der Volumenanteile
von schaltbaren Domänen beider ferroelektrischer Modifikationen
wird deutlich, dass die nicht-180 0 Domänenwandbeweglichkeit
in tetragonalem PZT sehr viel niedriger ist als in rhomboedrischem.
DF 6.3 Do 10:50 H11
Electrical fatigue of PZT ferroelectric films: in-situ structural
investigations — •J.L. Cao 1 , U. Klemradt 1 , A. Solbach 1 , U.
Böttger 2 , U. Ellerkmann 2 , P. Gerber 2 , P. J. Schorn 2 , and
R. Waser 2 — 1 II. Physikalisches Inst., RWTH Aachen, Germany —
2 Institut für Werkstoffe der Elektrotechnik 2, RWTH Aachen, Germany
Synchrotron radiation from Hasylab was used to study the structural
evolution of thin ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT) films under the influence
of an external AC field. In order to be sensitive to the evolution
of structural disorder or transitional layers at the electrode/PZT interfaces,
grazing incidence x-ray reflectivity was used instead of conventional
diffraction. Reflectivity curves were measured under in-situ conditions for
up to 108 electrical cycles, corresponding to different fatigue states. The
simulation of the reflectivity curves points at the growth of a very thin
Pt/PZT interfacial transition layer that is possibly correlated with the
electrical fatigue of the capacitor structure. The relationship between ferroelectric
fatigue and structural features of PZT thin films is discussed
with emphasis on the possibility of a mechanism which develops disorder
at the interface and contributes to the observed electrical properties.
DF 6.4 Do 11:10 H11
The contribution of misfit dislocations to polarization instabilities
of epitaxial ferroelectric Pb(Zr 0.52 Ti0.48)O 3 nanoislands —
M.-W. Chu, I. Szafraniak, R. Scholz, C. Harnagea, M. Alexe,
and •D. Hesse — Max-Planck-Institut für Mikrostrukturphysik Halle
(001)-oriented Pb(Zr 0.52 Ti0.48)O 3 (PZT) epitaxial nanoislands of d≈
9 nm average height were grown on niobium-doped SrTiO3 (001) substrates
(STO:Nb) by chemical solution deposition (CSD) at 800 ◦ C. Due
to the lattice mismatch, edge-type misfit dislocations are formed at
the PZT/STO:Nb interface. Using high-resolution electron microscopy
(HREM), the nature of these misfit dislocations has been analyzed, resulting
in a Burgers vector b a〈100〉. Applying the geometric phase imag-