Large scale domain switching around the tip of an impermeable stationary crack in ferroelectric ceramics driven by near-coercive electric field

It is widely accepted that the singular term plays a leading role in driving domain switching around the crack tip of ferroelectric ceramics.When an applied electric field approaches or even exceeds the coercive one,however,non-singular terms are no longer negligible and the switching of a large or global scale takes place.To analyze the large scale switching,one has to get a full asymptotic solution to the electric field in the vicinity of the crack tip.Take a double cantilever beam specimen as an example....     

Influence of an external electric field on the motion of a ferroelectric domain wall

The study of the influence of an external electric field on the motion from rest of a domain wall in ferroelectric crystals is presented. The solution of the problem representing the translational and rotational motions of the chain is sought in terms of solitary waves. Both electric and mechanical state of the structure in domains can be determined. The evolution of the velocity of the wall altered by the applied field is determined by means of energy arguments accounting for electromechanical couplings. A numerical simulation is given which illustrates the transient motion from rest of a wall separating two ferroelectric domains.     

Deformation of a ferroelectric smectic film in an electric field

Mechanisms of static deformation of a freely suspended ferroelectric smectic (C*) film in an external transverse electric field are analyzed. An equation for the shape of the film that includes the interaction of the applied field with the polarization vector and surface charges is derived in terms of the variational approach. The effect of deformation is shown to be of threshold character, which agrees with the experimental data.     

Reversible polarization of ferroelectric ceramics in a rapid-growing electric field

The complex permittivity of ferroelectric PZT ceramics with different compositions was measured in a pulsed rapid-growing electric field. The time dependence of the real component exhibits three peaks. The dips between them correlate with imaginary component peaks. Domain mechanisms that contribute to the ferroelectric polarization and are responsible for the time dependences are considered.     

Durability of polycrystalline ferroelectric ceramics in a constant electric field

The kinetics of mechanical fracture and electric breakdown of polycrystalline ferroelectric ceramics under simultaneous action of an electric field and mechanical load have been investigated. The procedures for determining the activation characteristics of both processes from only the fracture kinetics in one of them have been developed.     

Anomalous orientation of ferroelectric liquid crystal films in an electric field

An anomalous orientation of ferroelectric liquid crystals in an electric field is observed. The tilt planes of the molecules are oriented in a direction parallel to the electric field. The anomalous orientation is observed in freely suspended films above the smectic-C*-smectic-A bulk phase transition temperature. The effect is explained by the appearance of giant flexoelectric polarization, 10⁴ times greater than that in bulk liquid-crystal samples, in the film. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 414–418 (25 September 1997)     

Dynamics of domain-wall motion in ferroelectric liquid crystals in an electric field

The director reorientation in smectic liquid crystals with ferroelectric properties has been considered in the case where the interaction of liquid-crystal molecules with the surface leads to a partial unwinding of the helical structure of the liquid crystal and the reorientation occurs as a result of the domain-wall motion. The dependences of the velocity of domain-wall motion on the electric field strength, electric field variation frequency, boundary conditions, spontaneous polarization, and viscosity of the liquid crystal have been determined. It has been demonstrated that an increase in the electric field variation frequency or the polar part of the anchoring energy and the spontaneous polarization of the liquid crystal at a constant field frequency results in an increase of the velocity of domain-wall motion. As a consequence, the time of the electro-optic response of the liquid crystal in weak electric fields (from 0.4 to 2.0 V/μm) decreases by a factor of more than three.     

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.     

Nanoscale imaging of ferroelectric domain and resistance switching in hybrid improper ferroelectric Ca3Ti2O7 thin films

Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions such as the rotation and tilting of Ti-O octahedral in Ca₃Ti₂O₇ (CTO) family. In this work, we prepared different thickness CTO thin films on Pt substrates by pulsed laser deposition, and investigated their ferroelectric polarization reversal and the current transport properties by using the piezoresponse force microscopy and conducting atomic force microscopy, respectively. It is found that the CTO films exhibit clear ferroelectric domain switching and ferroelectric resistance switching behaviors, and the maximum resistive ratios of CTO film reaches ∼1750. These results demonstrate that hybrid improper ferroelectrics CTO films are promising materials for being employed in non-volatile memory and logic devices.     

Direct observation of switching processes in permalloy rings with lorentz microscopy

To achieve a deeper understanding of the switching process of magnetic Permalloy rings, Lorentz electron microscopy (LTEM) is used for the first time to image the magnetic configuration of such rings under applied external field conditions. Because of the exceptionally high lateral resolution we find two clearly distiguishable wall configurations present in the so-called "onion state." Furthermore, we show that a bias field present during a remagnetization cycle prevents the rings from transforming into a flux closure state, in which case remagnetization is a pure domain wall motion process.     

Behavior of a lead scandium tantalate ferroelectric in an ac electric field

The behavior of an incompletely ordered lead scandium tantalate ferroelectric (the degree of ordering s=0.8) in the region of the spontaneous ferroelectric transition is studied in ac electric fields by dielectric and optical methods. Dielectric nonlinearity of two types is observed. In fields above 2 kV/cm, the nonlinearity is caused by induced polarization effects and macrohysteresis behavior, whereas in weak fields, it is most probably associated with the dynamics of domain walls and/or phase boundaries.     

Electrocaloric response of a ferroelectric capacitor to a periodic electric field

The electrocaloric response of a ferroelectric capacitor to a periodic electric field has been analyzed in terms of the nonstationary heat conduction equation. A linear physical model is considered for an electrocaloric element in which one end (x = 0) is thermally insulated and a constant temperature T ₀ is maintained at the boundary x = l. The effect of a periodic electric field on the capacitor gives rise to temperature oscillations about a decreasing average value that reaches saturation. A relatively simple analytic expression is derived for the temperature distribution along the electrocaloric element and the heat flux density under stationary conditions. The calculations are carried out using the results obtained from measurements performed for a PMN-PT relaxor ferroelectric in the temperature range of the phase transition. A temperature gradient and a heat flux of ～150 W/cm² are observed in an electric field of 2.4 V/μm at a frequency of 10 Hz.     

Variation of the soft-mode frequency in ferroelectric semiconductors in a static electric field

The action of a static electric field on the soft-mode frequency in narrow-gap ferroelectric semiconductors, as a result of the contribution of the electron subsystem, is investigated within the framework of the vibronic mechanism. It is shown that the frequency of the soft mode varies directly as the square of the electric field strength under the action of the field, and the soft-mode frequency is determined in the vibronic model by the electron distribution function, whose parameters also vary under the action of the electric field. The effect is stronger for crystals with a one-dimensional electron spectrum than for those with an isotropic three-dimensional spectrum; according to estimates for ferroelectric semiconductors of the type Pb_1–xGe_xTe, a frequency variation of the order of the soft-mode frequency itself is attained in fields of the order of tens of volts per centimeter.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 33–37, January, 1988.     

Magnetism manipulation in ferromagnetic/ferroelectric heterostructures by electric field induced strain

Magnetization manipulation by an electric field(E-field) in ferromagnetic/ferroelectric heterostructures has attracted increasing attention because of the potential applications in novel magnetoelectric devices and spintronic devices, due to the ultra-low power consumption of the process. In this review, we summarize the recent progress in E-field controlled magnetism in ferromagnetic/ferroelectric heterostructures with an emphasis on strain-mediated converse magnetoelectric coupling. Firstly, we briefly review the history, the underlying theory of the magnetoelectric coupling mechanism, and the current status of research. Secondly, we illustrate the competitive energy relationship and volatile magnetization switching under an E-field. We then discuss E-field modified ferroelastic domain states and recent progress in non-volatile manipulation of magnetic properties. Finally, we present the pure E-field controlled 180° in-plane magnetization reversal and both E-field and current modified 180° perpendicular magnetization reversal.     

Direct observation of the proliferation of ferroelectric loop domains and vortex-antivortex pairs

We discovered stripe patterns of trimerization-ferroelectric domains in hexagonal REMnO(3) (RE=Ho,···,Lu) crystals (grown below ferroelectric transition temperatures (T(c)), reaching up to 1435 °C), in contrast with the vortex patterns in YMnO(3). These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below T(c), but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross T(c) even though the phase transition appears to not be Kosterlitz-Thouless-type. The experimental systematics are compared with the results of our six-state clock model simulation and also the Kibble-Zurek mechanism for trapped topological defects.     

Dielectric properties of KDP-type ferroelectric crystals in the presence of external electric field

Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities, temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease with electric field.     

In situ TEM observation of the nucleation and growth of silver oxide nanoparticles

The nucleation, growth, and coalescence of silver oxide nanoparticles have been investigated dynamically and at high spatial resolution by using the electron beam of a transmission electron microscope to stimulate and to observe the processes. Under the assumption the particles are hemispherical, the growth rate was found to be proportional to the square root of the electron irradiation time. This result suggests that the rate-limiting step is the attachment of atoms to the nanoparticles. Growth of the nanoparticles occurred by the addition of columns of atoms on {111} planes. Particle impingement resulted in interpenetration of the particles and, ultimately, the formation of a grain boundary.     

Interaction of nuclear spins with a time-dependent electric field in ferroelectric KNbO3

The effect of transitions in the nuclear spin system on the motion of the electric polarization in ferroelectric potassium niobate is studied theoretically. The equations of motion of the polarization are derived with inclusion of the interaction of the polarization with the nuclear spins and employed to calculate the contribution from nuclear transitions to the dielectric susceptibility of the crystal. This contribution has resonance maxima at the frequencies of nuclear transitions and is proportional to the square of the background dielectric susceptibility of the crystal. For the ferroelectric, this contribution is far larger than for earlier studied nonferroelectric dielectrics. Numerical estimates show that, in potassium niobate, the contribution from the nuclei to the dielectric susceptibility is of the same order of magnitude as that to the magnetic susceptibility.