摘要:

A lattice-Monte Carlo approach was developed to simulate ferroelectric domain behavior. The model utilizes a Hamiltonian for the total energy that includes electrostatic terms (involving dipole-dipole interactions, local polarization gradients, and applied electric field), and elastic strain energy. The contributions of these energy components to the domain structure and to the overall applied field response of the system were examined. In general, the model exhibited domain structure characteristics consistent with those observed in a tetragonally distorted ferroelectric. Good qualitative agreement between the appearance of simulated electrical hysteresis loops and those characteristic of real ferroelectric materials was found. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324454

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We report a dramatic influence of lithium nonstoichiometry inLiTaO3crystals on the 180° coercive fields, internal fields, domain wall strain, optical birefringence, and domain shape. Congruent composition ofLiTaO3([Li]/([Li]+[Ta])∼0.485)show large coercive fields of ∼21 kV/mm for domain motion and built-in internal fields of ∼4.5 kV/mm, domain wall strains of|&Vegr;zz|∼(1–10)×10−6,optical birefringence in the z-plane, and triangular domains with domain walls parallel to the crystallographic x-axes. On the other hand, near-stoichiometric crystals ofLiTaO3([Li]/([Li]+[Ta])∼0.499)studied here show low coercive fields of ∼1.7 kV/mm, internal fields of <0.1 kV/mm, negligible domain wall strain or optical birefringence, and six-sided domains with domain walls parallel to crystallographicy-axes. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324455

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In situtransmission electron microscopy of domain motion in thinnedBaTiO3andKNbO3shows that curved ferroelectric domains move more readily under low electric fields than do straight domain walls. We show that this relative motility arises because curved domain walls support a Maxwellian displacement charge and therefore experience a direct pressure that is proportional to the electric fieldE. Conversely, untilted charge-neutral domain walls experience a pressure proportional toE3due to induced displacement charge, and therefore tend to resist motion at low fields. Any physical process that leads to an increase in density of the immobile charge-free domain walls, relative to the more mobile curved domain walls, could lead to an increase in overall resistance to domain switching, providing an intrinsic contribution to ferroelectric fatigue. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324456

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We report the experimental studies of the vibrational spectra ofSrTiO3films grown by pulsed laser deposition. Raman scattering, with and without bias electric field, and Fourier-transform far-infrared ellipsometry between 30 and 700 cm−1have been utilized for investigation of the phonon behavior. These results are discussed in connection with the low-frequency dielectric properties of theSrTiO3films. In the films, the soft mode reveals hardening compared to that in bulk crystals. This observation is in agreement with the Lyddane-Sachs-Teller formalism. The existence of local polar regions is proposed as an important factor determining the dielectric properties of ferroelectric thin films. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324457

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We study the domain structure in ferroelectric thin films with a ‘passive’ layer (material with damaged ferroelectric properties) at the interface between the film and electrodes within a continuous medium approximation. An abrupt transition from a monodomain to a polydomain state has been found with the increase of the ‘passive’ layer thicknessd. The domain width changes very quickly at the transition (exponentially withd−2). Similar behavior is obtained for epitaxial ferroelectric (without top electrode) and ferroelastic films. We have estimated the dielectric responsedP/dE(the slope of the hysteresis loop) in the ‘fatigued’ multidomain state and found that it is in agreement with experiment, assuming realistic parameters of the layer. We derive a simple universal relation for the dielectric response, which scales as1/d,involving only the properties of the passive layer. This relation qualitatively reproduces the evolution of the hysteresis loop in fatigued samples and it could be tested with controlled experiments. It is expected that the coercive field should increase with decreasing lateral size of the film. We believe that specific properties of the domain structure under bias voltage in ferroelectrics with a passive layer can resolve the long-standing ‘paradox of the coercive field.’ ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324458

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We consider ferroelectric phase transitions in both short-circuited and biased ferroelectric-semiconductor films with a space (depletion) charge which leads to some unusual behavior. It is shown that in the presence of the charge the polarization separates into ‘switchable’ and ‘non-switchable’ parts. The electric field, appearing due to the space charge, does not wash out the phase transition, which remains second order but takes place at somewhat reduced temperature. At the same time, it leads to a suppression of the ferroelectricity in a near-electrode layer. Influence of the depletion charge on thermodynamic coercive field reduces mainly to the lowering of the phase transition temperature, and its effect is negligible. The depletion charge can, however, facilitate an appearance of the domain structure which would be detrimental for device performance (fatigue). ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324459

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The longitudinal Brillouin back-scattering spectra, dielectric permittivities and polarization-electric field (P-E) hysteresis loops along the [111] direction have been measured as a function of temperature for a relaxor ferroelectric single crystal(PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33(PMN-33&percent;PT). A sharp ferroelectric phase transition, which is associated with a minimum in phonon frequency and an abrupt change in polarization, was observed near 425 K. As temperature decreases, a diffuse phase transition which is associated with a broad frequency-dependent dielectric spectrum and a gradual evolution in polarization, was detected near 350 K. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 350 and 425 K) are diffuse first-order and first-order, respectively. The field-cooled-zero-field-heated dielectric permittivities show that the dc bias field induces a long-range ferroelectric phase transition at 357 K and imply the phase coexistence of a short-range electric ordering and a long-range electric ordering in the region of ∼330–380 K. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324460

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The power law behaviors implied by the Cole-Cole plot are presented. The power law behavior in the frequency domain, indicated by the shape of the Cole-Cole plot, implies power law behavior in the time domain as well. The so-called “delayed response” in &egr;(&ohgr;) should be interpreted as a long time transient response, which can impose significant experimental constraints. Dielectric materials in general, and ferroelectric crystals in particular, allow us to investigate power law decay in great detail and offer an experimental probe into a very fundamental question does power law behavior necessarily imply a fractal underlying structure? ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324461

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A theoretical analysis of the ground state of long-chain(K&at;C60)nis presented. Within mean field theory, a ferroelectric ground state is found to be stable because of the pseudo-Jahn-Teller mixing of theb1uand theb2gband with a zone-center optical phonon involving the displacement of the endohedralK−ions. A phase diagram for this model is derived in the narrow bandwidth regime. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324462

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The temperature dependence of the relaxation time distribution functiong(&tgr;)was obtained from a Tikhonov regularization analysis of dielectric loss data in the dipole glass DRADP-x(x=0.47).A crossover region of the relaxation dynamics was evidenced in the temperature region of40&hthinsp;K±2&hthinsp;Kfrom a distinct change in the shape ofg(&tgr;).We attempt to explain this crossover phenomenon in terms of a dynamically correlated domains (DCDs) model. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324463

出版商:AIP    

年代:1900

数据来源: AIP