298 research outputs found
Structural phase transition and dielectric relaxation in Pb(Zn1/3Nb2/3)O3 single crystals
The structure and the dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN) crystal
have been investigated by means of high-resolution synchrotron x-ray
diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in
the frequency range of 100 Hz - 1 MHz). At high temperatures, the PZN crystal
exhibits a cubic symmetry and polar nanoregions inherent to relaxor
ferroelectrics are present, as evidenced by the single (222) Bragg peak and by
the noticeable tails at the basis of the peak. At low temperatures, in addition
to the well-known rhombohedral phase, another low-symmetry, probably
ferroelectric, phase is found. The two phases coexist in the form of mesoscopic
domains. The para- to ferroelectric phase transition is diffused and observed
between 325 and 390 K, where the concentration of the low-temperature phases
gradually increases and the cubic phase disappears upon cooling. However, no
dielectric anomalies can be detected in the temperature range of diffuse phase
transition. The temperature dependence of the dielectric constant show the
maximum at higher temperature (Tm = 417 - 429 K, depending on frequency) with
the typical relaxor dispersion at T < Tm and the frequency dependence of Tm
fitted to the Vogel-Fulcher relation. Application of an electric field upon
cooling from the cubic phase or poling the crystal in the ferroelectric phase
gives rise to a sharp anomaly of the dielectric constant at T 390 K and
diminishes greatly the dispersion at lower temperatures, but the dielectric
relaxation process around Tm remains qualitatively unchanged. The results are
discussed in the framework of the present models of relaxors and in comparison
with the prototypical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3.Comment: PDF file, 13 pages, 6 figures collected on pp.12-1
Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3
The microstructure and phase transition in relaxor ferroelectric
Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain
to be one of the most puzzling issues of solid state science. In the present
work we have investigated the evolution of the phase symmetry in PMN-xPT
ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <=
x <= 0.15) by means of high-resolution synchrotron x-ray diffraction.
Structural analysis based on the experimental data reveals that the
substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in
the development of a clean rhombohedral phase at a PT-concentration as low as
5%. The results provide some new insight into the development of the
ferroelectric order in PMN-PT, which has been discussed in light of the
kinetics of polar nanoregions and the physical models of the relaxor
ferroelectrics to illustrate the structural evolution from a relaxor to a
ferroelectric state.Comment: Revised version with updated references; 9 pages, 4 figures embedde
Monte Carlo Study of Relaxor Systems: A Minimum Model for Pb(InNb)O}
We examine a simple model for Pb(InNb)O (PIN), which
includes both long-range dipole-dipole interaction and random local anisotropy.
A improved algorithm optimized for long-range interaction has been applied for
efficient large-scale Monte Carlo simulation. We demonstrate that the phase
diagram of PIN is qualitatively reproduced by this minimum model. Some
properties characteristic of relaxors such as nano-scale domain formation, slow
dynamics and dispersive dielectric responses are also examined.Comment: 5 pages, 4 figure
Direct observation of the formation of polar nanoregions in Pb(MgNb)O using neutron pair distribution function analysis
Using neutron pair distribution function (PDF) analysis over the temperature
range from 1000 K to 15 K, we demonstrate the existence of local polarization
and the formation of medium-range, polar nanoregions (PNRs) with local
rhombohedral order in a prototypical relaxor ferroelectric
Pb(MgNb)O. We estimate the volume fraction of the PNRs as a
function of temperature and show that this fraction steadily increases from 0 %
to a maximum of 30% as the temperature decreases from 650 K to 15 K.
Below T200 K the PNRs start to overlap as their volume fraction reaches
the percolation threshold. We propose that percolating PNRs and their
concomitant overlap play a significant role in the relaxor behavior of
Pb(MgNb)O.Comment: 4 pages, 3 figure
Spatially Resolved Mapping of Local Polarization Dynamics in an Ergodic Phase of Ferroelectric Relaxor
Spatial variability of polarization relaxation kinetics in relaxor
ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved
Piezoresponse Force Microscopy. Local relaxation attributed to the
reorientation of polar nanoregions is shown to follow stretched exponential
dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the
macroscopic value determined from dielectric spectra (beta~~0.09). The spatial
inhomogeneity of relaxation time distributions with the presence of 100-200 nm
"fast" and "slow" regions is observed. The results are analyzed to map the
Vogel-Fulcher temperatures on the nanoscale.Comment: 23 pages, 4 figures, supplementary materials attached; to be
submitted to Phys. Rev. Let
Optically Isotropic and Monoclinic Ferroelectric Phases in PZT Single Crystals near Morphotropic Phase Boundary
We report the finding of unusual scale-dependent symmetry below the
ferroelectric Curie temperature in the perovskite Pb(Zr1-xTix)O3 single
crystals of morphotropic phase boundary compositions. The crystals of
tetragonal symmetry (from x-ray diffraction experiments) on sub-micrometer
scale exhibit a macroscopic (optically determined) cubic symmetry. This
peculiar optical isotropy is explained by the anomalously small size of
tetragonal ferroelectric domains. Upon further cooling the crystals transform
to the phase consisting of micrometer-sized domains of monoclinic Cm symmetry.Comment: 7 pages, 3 figure
Dielectric nonlinearity of relaxor ferroelectric ceramics at low ac drives
Dielectric nonlinear response of
(PbMgNbO)(PbTiO) (0.9PMN-0.1PT) relaxor
ceramics was investigated under different ac drive voltages. It was observed
that: (i) the dielectric permittivity is independent on ac field amplitude at
high temperatures; (ii) with increasing ac drive, the permittivity maximum
increases, and the temperature of the maximum shifts to lower temperature;
(iii) the nonlinear effect is weakened when the measurement frequency
increases. The influences of increasing ac drive were found to be similar to
that of decreasing frequency. It is believed that the dielectric nonlinearities
of relaxors at low drives can be explained by the phase transition theory of
ergodic space shrinking in succession. A Monte Carlo simulation was performed
on the flips of micro polarizations at low ac drives to verify the theory.Comment: Submitted to J. Phys.: Cond. Matte
Barkhausen Noise in a Relaxor Ferroelectric
Barkhausen noise, including both periodic and aperiodic components, is found
in and near the relaxor regime of a familiar relaxor ferroelectric,
PbMgNbO, driven by a periodic electric field. The
temperature dependences of both the amplitude and spectral form show that the
size of the coherent dipole moment changes shrink as the relaxor regime is
entered, contrary to expectations based on some simple models.Comment: 4 pages RevTeX4, 5 figures; submitted to Phys Rev Let
Block-modular technology training in the discipline of «Electromagnetic fields and waves» using learning management system «Moodle»
The results of the development and implementation of block-modular technology in the learning process of students using a learning management system "MOODLE" in the example, the academic discipline of "Еlectromagnetic fields and waves".Изложены результаты разработки и внедрения блочно-модульной технологии в процесс обучения студентов с использованием системы управления обучением «МOODLE» на примере учебной дисциплины «Электромагнитные поля и волны»
Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3
Neutron inelastic scattering measurements of the polar TO phonon mode
dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal
anomalous behavior in which the optic branch appears to drop precipitously into
the acoustic branch at a finite value of the momentum transfer q=0.2 inverse
Angstroms, measured from the zone center. We speculate this behavior is the
result of nanometer-sized polar regions in the crystal.Comment: 4 pages, 4 figure
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