263 research outputs found
Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries
Migration of charged point defects triggered by the local random
depolarization field is shown to plausibly explain aging of poled ferroelectric
ceramics providing reasonable time and acceptor concentration dependences of
the emerging internal bias field. The theory is based on the evaluation of the
energy of the local depolarization field caused by mismatch of the
polarizations of neighbor grains. The kinetics of charge migration assumes
presence of mobile oxygen vacancies in the material due to the intentional or
unintentional acceptor doping. Satisfactory agreement of the theory with
experiment on the Fe-doped lead zirconate titanate is demonstrated.Comment: theory and experiment, 22 pages, 3 figure
Effect of uniaxial stress on ferroelectric behavior of (Bi1/2Na1/2)TiO3-based lead-free piezoelectric ceramics
Prior studies have shown that a field-induced ferroelectricity in ceramics with general chemical formula (1-x-y) (Bi1/2 Na1/2) TiO3 -x BaTiO3 -y (K0.5 Na0.5) NbO3 and a very low remanent strain can produce very large piezoelectric strains. Here we show that both the longitudinal and transverse strains gradually change with applied electric fields even during the transition from the nonferroelectric to the ferroelectric state, in contrast to known Pb-containing antiferroelectrics. Hence, the volume change and, in turn, the phase transition can be affected using uniaxial compressive stresses, and the effect on ferroelectricity can thus be assessed. It is found that the 0.94 (Bi1/2 Na1/2) TiO3 -0.05 BaTiO3 -0.01 (K0.5 Na0.5) NbO3 ceramic (largely ferroelectric), with a rhombohedral R3c symmetry, displays large ferroelectric domains, significant ferroelastic deformation, and large remanent electrical polarizations even at a 250 MPa compressive stress. In comparison, the 0.91 (Bi1/2 Na1/2) TiO3 -0.07 BaTiO3 -0.02 (K0.5 Na0.5) NbO3 ceramic (largely nonferroelectric) possesses characteristics of a relaxor ferroelectric ceramic, including a pseudocubic structure, limited ferroelastic deformation, and low remanent polarization. The results are discussed with respect of the proposed antiferroelectric nature of the nonferroelectric state.open291
Electric-field-induced antiferroelectric to ferroelectric phase transition in mechanically confined Pb0.99Nb0.02[(Zr0.57Sn0.43)(0.94)Ti-0.06](0.98)O-3
The electric-field-induced phase transition was investigated under mechanical confinements in bulk samples of an antiferroelectric perovskite oxide at room temperature. Profound impacts of mechanical confinements on the phase transition are observed due to the interplay of ferroelasticity and the volume expansion at the transition. The uniaxial compressive prestress delays while the radial compressive prestress suppresses it. The difference is rationalized with a phenomenological model of the phase transition accounting for the mechanical confinement.open241
Domain switching energies: Mechanical versus electrical loading in La-doped bismuth ferrite-lead titanate
The mechanical stress-induced domain switching and energy dissipation in morphotropic phase boundary (1 - x)(Bi(1-y)La(y))FeO(3)-xPbTiO(3) during uniaxial compressive loading have been investigated at three different temperatures. The strain obtained was found to decrease with increasing lanthanum content, although a sharp increase in strain was observed for compositions doped with 7.5 and 10 at. % La. Increased domain switching was found in compositions with decreased tetragonality. This is discussed in terms of the competing influences of the amount of domain switching and the spontaneous strain on the macroscopic behavior under external fields. Comparison of the mechanically and electrically dissipated energy showed significant differences, discussed in terms of the different microscopic interactions of electric field and stress.open10
Stratified spatiotemporal chaos in anisotropic reaction-diffusion systems
Numerical simulations of two dimensional pattern formation in an anisotropic
bistable reaction-diffusion medium reveal a new dynamical state, stratified
spatiotemporal chaos, characterized by strong correlations along one of the
principal axes. Equations that describe the dependence of front motion on the
angle illustrate the mechanism leading to stratified chaos
Phase chaos in the anisotropic complex Ginzburg-Landau Equation
Of the various interesting solutions found in the two-dimensional complex
Ginzburg-Landau equation for anisotropic systems, the phase-chaotic states show
particularly novel features. They exist in a broader parameter range than in
the isotropic case, and often even broader than in one dimension. They
typically represent the global attractor of the system. There exist two
variants of phase chaos: a quasi-one dimensional and a two-dimensional
solution. The transition to defect chaos is of intermittent type.Comment: 4 pages RevTeX, 5 figures, little changes in figures and references,
typos removed, accepted as Rapid Commun. in Phys. Rev.
Frequency-dependence of large-signal properties in lead-free piezoceramics
The dependence of large signal properties of (1-x)(0.81Bi 1/2Na 1/2TiO 3-0.19Bi 1/2K 1/2TiO 3)-xBi(Zn 1/2Ti 1/2)O 3 with x 0.02, 0.03, and 0.04 on the measurement frequency was investigated for a wide range of frequencies from 0.1 Hz to 100 Hz. A significant frequency dispersion in the characteristic parameters representatively maximum and coercive values was denoted. On extension with the temperature dependent dielectric permittivity measurement, it was shown that the observed frequency dependence is primarily correlated with the dynamics of field-induced phase transition from a relaxor state to a long-range ferroelectric state. Increasing the substitutional disorder introduced by Bi(Zn 1/2Ti 1/2)O 3 addition was demonstrated to pronounce the frequency dependence. It was proposed that the change be due to the increase in random fields and consequent dominance of ergodicity, based on the frequency-dependent hysteresis measurements at an elevated temperature above so-called induced-ferroelectric-to-relaxor transition temperature.open8
Modeling of dielectric hysteresis loops in ferroelectric semiconductors with charged defects
We have proposed the phenomenological description of dielectric hysteresis
loops in ferroelectric semiconductors with charged defects and prevailing
extrinsic conductivity. Exactly we have modified Landau-Ginsburg approach and
shown that the macroscopic state of the aforementioned inhomogeneous system can
be described by three coupled equations for three order parameters. Both the
experimentally observed coercive field values well below the thermodynamic one
and the various hysteresis loop deformations (constricted and double loops)
have been obtained in the framework of our model. The obtained results
quantitatively explain the ferroelectric switching in such ferroelectric
materials as thick PZT films.Comment: 21 pages, 10 figures, sent to Journal of Physics: Condensed Matte
Random Matrix Theories in Quantum Physics: Common Concepts
We review the development of random-matrix theory (RMT) during the last
decade. We emphasize both the theoretical aspects, and the application of the
theory to a number of fields. These comprise chaotic and disordered systems,
the localization problem, many-body quantum systems, the Calogero-Sutherland
model, chiral symmetry breaking in QCD, and quantum gravity in two dimensions.
The review is preceded by a brief historical survey of the developments of RMT
and of localization theory since their inception. We emphasize the concepts
common to the above-mentioned fields as well as the great diversity of RMT. In
view of the universality of RMT, we suggest that the current development
signals the emergence of a new "statistical mechanics": Stochasticity and
general symmetry requirements lead to universal laws not based on dynamical
principles.Comment: 178 pages, Revtex, 45 figures, submitted to Physics Report
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