1,215 research outputs found
Electronic structure and bond competition in the polar magnet PbVO
Density functional electronic structure studies of tetragonal PbVO are
reported. The results show a an important role for both Pb 6 - O 2 and V
- O bonding, with an interplay between these. This is discussed in
relation to the possibility of obtaining magnetoelectric behavior.Comment: 5 page
Nano-scale oxygen octahedral tilting in 0.90(Bi1/2Na1/2)TiO3-0.05(Bi1/2K1/2)TiO3-0.05BaTiO3 lead-free perovskite piezoelectric ceramics
The oxygen octahedral tilted domains in
0.90(Bi1/2Na1/2)TiO3-0.5(Bi1/2K1/2)TiO3-0.5BaTiO3 lead-free perovskite
piezoelectric ceramic have been studied by transmission electron microscopy
(TEM). Selected-area electron diffraction patterns shows the 1/2ooo and 1/2ooe
reflections, indicating the presence of antiphase (a-a-a-) and in-phase
(aoaoc+) octahedral tilting, respectively. The morphology and distributions of
these tilted domains are shown in the centered dark-field images. Further, the
Bragg-filtered high-resolution TEM image reveals that the size of the in-phase
tilted domains varies from 1 to 8 nm across. The ceramic contains the mixture
of non-tilted and variants of the antiphase and in-phase tilted domains.Comment: 12 pages, 3 figure
Poling effect on distribution of quenched random fields in a uniaxial relaxor ferroelectric
The frequency dependence of the dielectric permitivity's maximum has been
studied for poled and unpoled doped relaxor strontium barium niobate
(SBN-61:Cr). In both cases the maximum
found is broad and the frequency dispersion is strong. The present view of
random fields compensation in the unpoled sample is not suitable for explaining
this experimental result. We propose a new mechanism where the dispersion of
quenched random electric fields, affecting the nanodomains, is minimized after
poling. We test our proposal by numerical simulations on a random field Ising
model. Results obtained are in agreement with the polarization's measurements
presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].Comment: 7 pages, 4 figure
CaCu_3Ti_4O_12/CaTiO_3 Composite Dielectrics: A Ba/Pb-free Ceramics with High Dielectric Constants
We have measured dielectric properties of CaCuTiO
( = 0, 0.1, 0.5, 1, 1.5, 2, 2.9 and 3), and have found that
CaCuTiO (a composite of CaCuTiO and
CaTiO) exhibits a high dielectric constant of 1800 with a low dissipation
factor of 0.02 below 100 kHz from 220 to 300 K. These are comparable to (or
even better than) those of the Pb/Ba-based ceramics, which could be attributed
to a barrier layer of CaTiO on the surface of the CaCuTiO
grains. The composite dielectric ceramics reported here are environmentally
benign as they do not contain Ba/Pb.Comment: 4 pages, 4 figures, Appl. Phys. Lett. (scheduled on July 25, 2005
Inhomogeneous Magnetoelectric Effect on Defect in Multiferroic Material: Symmetry Prediction
Inhomogeneous magnetoelectric effect in magnetization distribution
heterogeneities (0-degree domain walls) appeared on crystal lattice defect of
the multiferroic material has been investigated. Magnetic symmetry based
predictions of kind of electrical polarization distribution in their volumes
were used. It was found that magnetization distribution heterogeneity with any
symmetry produces electrical polarization. Results were systemized in scope of
micromagnetic structure chirality. It was shown that all 0-degree domain walls
with time-noninvariant chirality have identical type of spatial distribution of
the magnetization and polarization.Comment: submitted to IOP Conference Series: Materials Science and Engineerin
Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films
We have grown lead iron niobate thin films with composition Pb(Fe1/2Nb1/2)O3
(PFN) on (0 0 1) SrTiO3 substrates by pulsed laser deposition. The influence of
the deposition conditions on the phase purity was studied. Due to similar
thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN
perovskite phase. By optimizing the kinetic parameters, we succeeded in
identifying a deposition window which resulted in epitaxial perovskite-phase
PFN thin films with no identifiable trace of impurity phases appearing in the
X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were
smooth and epitaxially oriented with the substrate and as demonstrated by RHEED
streaks which were aligned with the substrate axes. X-ray diffraction showed
that the films were completely c-axis oriented and of excellent crystalline
quality with low mosaicity (X-ray rocking curve FWHM<0.09). The surface
roughness of thin films was also investigated by atomic force microscopy. The
root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm
for 100-nm-thick films. We also observe a correlation between grain size,
surface roughness and film thickness.Comment: 13 Pages, 6 figures. To be published in J. Mag. Mag Mater.
proceedings of EMRS200
First-principles study of the ferroelectric Aurivillius phase Bi2WO6
In order to better understand the reconstructive ferroelectric-paraelectric
transition of Bi2WO6, which is unusual within the Aurivillius family of
compounds, we performed first principles calculations of the dielectric and
dynamical properties on two possible high-temperature paraelectic structures:
the monoclinic phase of A2/m symmetry observed experimentally and the
tetragonal phase of I4/mmm symmetry, common to most Aurivillius phase
components. Both paraelectric structures exhibits various unstable modes, which
after their condensation bring the system toward more stable structures of
lower symmetry. The calculations confirms that, starting from the paraelectric
A2/m phase at high temperature, the system must undergo a reconstructive
transition to reach the P2_1ab ferroelectric ground state.Comment: added Appendix and two table
Size effects in multiferroic BiFeO3 nanodots: A first-principles-based study
An effective Hamiltonian scheme is developed to investigate structural and
magnetic properties of BiFeO3 nanodots under short-circuit-like electrical
boundary conditions. Various striking effects are discovered. Examples include
(a) scaling laws involving the inverse of the dots' size for the magnetic and
electric transition temperatures; (b) the washing out of some structural phases
present in the bulk via size effects; (c) the possibility of tailoring the
difference between the Neel and Curie temperatures, by playing with the size
and electrical boundary conditions; and (d) an universal critical thickness of
the order of 1.6 nm below which the dots do not possess any long-range ordering
for the electrical and magnetic dipoles, as well as, for the oxygen octahedral
tiltings.Comment: 3 figure
Quadratic-in-magnetization permittivity and conductivity tensor in cubic crystals
We present diagonal and off-diagonal elements of the permittivity and
conductivity tensor up to the second order in magnetization for cubic crystals.
We express all tensor elements as a function of a general sample orientation,
for arbitrary magnetization direction and for (001), (011) and (111) surface
orientations. Finally, we discuss, how to extract values of quadratic elements
G of the second order permittivity tensors for different sample surface
orientations from both experiment and ab-initio calculations
Symmetry Theory of the Flexomagnetoelectric Interaction in the Magnetic Vortices and Skyrmions
Symmetry classification of the magnetic vortices and skyrmions has been
suggested. Relation between symmetry based predictions and direct calculation
has been shown. It was shown, that electric dipole moment of the vortex is
located inside the small vortex core. The antivortices and antiskyrmions do not
carry the total core electric dipole induced by the flexomagnetoelectric
interaction in the hexoctahedral cubic crystal. The volumetric bound electric
charge is distributed around the core. Switching of the core electric dipole
direction produces the switching of the core magnetization or vortex chirality
and vice versa. The vortices and skyrmions with time-invariant enantiomorphism
have two degenerative states: clockwise and counterclockwise state.Comment: Submitted revised version to the Physica B: Condenced Matte
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