19 research outputs found
Very large dielectric response of thin ferroelectric films with the dead layers
We study the dielectric response of ferroelectric (FE) thin films with "dead"
dielectric layer at the interface with electrodes. The domain structure
inevitably forms in the FE film in presence of the dead layer. As a result, the
effective dielectric constant of the capacitor increases
abruptly when the dead layer is thin and, consequently, the pattern of
180-degree domains becomes "soft". We compare the exact results for this
problem with the description in terms of a popular "capacitor" model, which is
shown to give qualitatively incorrect results. We relate the present results to
fatigue observed in thin ferroelectric films.Comment: 5 pages, REVTeX 3.1 with one eps-figure. A note added that the linear
response is not changed by electromechanical effect. To appear in Phys. Rev.
Simulations of cubic-tetragonal ferroelastics
We study domain patterns in cubic-tetragonal ferroelastics by solving
numerically equations of motion derived from a Landau model of the phase
transition, including dissipative stresses. Our system sizes, of up to 256^3
points, are large enough to reveal many structures observed experimentally.
Most patterns found at late stages in the relaxation are multiply banded; all
three tetragonal variants appear, but inequivalently. Two of the variants form
broad primary bands; the third intrudes into the others to form narrow
secondary bands with the hosts. On colliding with walls between the primary
variants, the third either terminates or forms a chevron. The multipy banded
patterns, with the two domain sizes, the chevrons and the terminations, are
seen in the microscopy of zirconia and other cubic-tetragonal ferroelastics. We
examine also transient structures obtained much earlier in the relaxation;
these show the above features and others also observed in experiment.Comment: 7 pages, 6 colour figures not embedded in text. Major revisions in
conten
Proper ferroelastic phase transitions in thin epitaxial films with symmetry-conserving and symmetry-breaking misfit strains
We study how the ferroelastic domain structure sets in in an epitaxial film
of a material with second order proper ferroelastic transition. The domain
structures considered are similar to either or
structures in perovskite ferroelectrics. If the "extrinsic" misfit
strain, not associated with the transition, does not break the symmetry of the
high-temperature phase, the phase transition in the film occurs at somewhat
lower temperature compared to the bulk. The loss of stability then occurs with
respect to a sinusoidal strain wave, which evolves into the domain structure
with practically the same geometry and approximately the same period. In the
presence of the symmetry-breaking component of the misfit strain ("extrinsic"
misfit) the character of the phase transition is qualitatively different. In
this case it is a {\em topological} transition between single-domain and
multi-domain states, which starts from a low density of the domain walls.Comment: 7 pages, 2 figures, REVTeX 3.
Anomalous enhancement of tetragonality in PbTiO3 induced by negative pressure
Using a first-principles approach based on density-functional theory, we find
that a large tetragonal strain can be induced in PbTiO3 by application of a
negative hydrostatic pressure. The structural parameters and the dielectric and
dynamical properties are found to change abruptly near a crossover pressure,
displaying a ``kinky'' behavior suggestive of proximity to a phase transition.
Analogous calculations for BaTiO3 show that the same effect is also present
there, but at much higher negative pressure. We investigate this unexpected
behavior of PbTiO3 and discuss an interpretation involving a phenomenological
description in terms of a reduced set of relevant degrees of freedom.Comment: 9 pages, with 9 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/st_pbti/index.htm
Strain sensitivity of polarization in perovskite ferroelectrics
The sensitivity of spontaneous polarization to epitaxial strains is evaluated for several perovskite ferroelectrics using the nonlinear thermodynamic theory. For BaTiO3, PbTiO3, and Pb (Zr 0.2 Ti0.8) O3 epitaxial layers subjected to large compressive in-plane strains, the predicted relative polarization changes agree with the results of first-principles calculations. This agreement shows that the strain sensitivity of polarization is predominantly governed by the linear electrostriction even at large strains. The calculations performed for Pb (Zr1-x Tix) O3 films of different compositions further demonstrate that the strain sensitivity strongly enhances near the morphotropic phase boundary, breaking the inverse correlation with the bulk polarization that was proposed earlier. © 2008 American Institute of Physics
Polarization-controlled spin reorientation transition and resistive switching in ferromagnetic-ferroelectric nanostructures and tunnel junctions
International audienceA spin reorientation transition (SRT) induced in a ferromagnetic nanolayer by the polarization switching in an adjoining ferroelectric film or bulk crystal is described theoretically. It is shown that such a polarization-controlled SRT can be realized in a narrow range of the nanolayer thicknesses only. Our calculations allowing for the polarization-dependent interfacial magnetic anisotropy predict that this " thickness window " is located between two threshold thicknesses, at which a size-induced SRT takes place in the ferromagnetic nanolayer at two different directions of the ferroelectric polarization. Importantly, the polarization-controlled SRT manifests itself in the resistance switching occurring in multiferroic tunnel junctions (MFTJs), where an ultrathin ferroelectric barrier is embedded between a ferromagnetic electrode with controllable magnetization and an electrode with a fixed magnetization. Using Fe/BaTiO 3 /Fe junctions as a representative example, we demonstrate that such MFTJs can be employed as electric-write nanoscale memory cells with reliable nondestructive readout and high thermal stability of information storage
Finite-element analysis of scattering parameters of surface acoustic wave bandpass filter formed on barium titanate thin film
Enhancing permittivity of ferroelectric superlattices via composition tuning
International audienc