Susceptibility Of Ferroelectrics Research Articles

Dynamics of nonlinear dielectric susceptibility of ferroelectrics near the morphotropic phase boundary

The dynamics of the nonlinear (NL) dielectric susceptibility of ferroelectrics (FE) near the morphotropic phase boundary (MPB) is theoretically investigated based on the Landau–Devonshire free energy approach and the concept of FE soft modes. To do so, the NL dielectric susceptibility elements of FE material in the tetragonal phase are expressed as functions of optical phonon modes. These are the E modes with normal characteristic frequency and the A modes with . On the one hand, the tetragonal E modes appear to exhibit a double soft-mode character, i.e. the mode softens either when the thermodynamic temperature T approaches the transition temperature Tc or when the free energy parameter β1 approaches β2. On the other hand, the A modes exhibit single soft-mode character when T approaches Tc. Within this formulation, the dynamics of first-, second- and third-order NL susceptibility elements are investigated. The origin of the anomalous behavior of certain NL elements at the MPB appears to be a manifestation of FE mode-softening. This approach provides a simple yet powerful technique to understand the dynamics of the NL dielectric susceptibility elements of FE material near the MPB.

Diffuse phase transition in ferroelectrics with mesoscopic heterogeneity: Mean-field theory

The diffuse phase transition in ferroelectrics with mesoscopic heterogeneity has been discussed within the context of a superparaelectric model by using the Ginzburg-Landau formalism. In the Curie region ferroelectrics with mesoscopic heterogeneity are treated as 'superparaelectrics' consisting of a mass of polar clusters, each of which has Ising character. Based on the mean-field theory, the influence of the finite-size effects of polar clusters on their structural instability has been discussed by considering a coherent lattice coupling between two structurally different regions. In particular, we have analytically derived the explicit solutions of the distribution of local polarizations. In turn, the processes of polar nanophase precipitation and coarsening have been also discussed in conjunction with the local chemical or structural inhomogeneity. Moreover, we have also analyzed the relationship between the local polarization distribution and the static dielectric susceptibility in ferroelectrics with the nanometric scale heterogeneity. The width of the Curie region is dependent upon the distribution of the sum of localized correlation length, which reflects the size distribution of heterogeneity. The presented analysis reveals that the diffuse phase transition is closely associated with the existence of nanometric polar clusters and their physical size distribution. Intriguingly, our theoretical results bear a very close resemblance to most experimental observations.

High-frequency, transient magnetic susceptibility of ferroelectrics

A significant high-frequency magnetic susceptibility was measured both in weakly polarized and nonpolarized samples of barium titanate, lead zirconate titanate, and carnauba wax. Magnetic susceptibility measurements were made from 10 to 500 MHz using a thin film permeameter at room temperature; initial susceptibilities ranged from 0.1 to 2.5. These values are larger than expected for paramagnets and smaller than expected for ferromagnets. It was found that the magnetic susceptibility decreases rapidly with exposure to the exciting field. The origin of the magnetic susceptibility is thought to originate with the applied time varying electric field associated with the susceptibility measurements. An electric field acts to rotate an electric dipole, creating a magnetic quadrupole if the two moments are balanced, and a net magnetic dipole moment if imbalanced. It is thought that local electrostatic fields created at ferroelectric domain discontinuities associated with grain boundaries create an imbalance in the anion rotation that results in a net, measurable, magnetic moment. The origin of the magnetic aftereffect may be due to the local heating of the material through the moving charges associated with the magnetic moment.

Size effect on the dielectric susceptibility of ferroelectrics

Abstract Using Landau theory, the influence of size on the dielectric behaviour of ferroelectric films, cylinders and spheres has been investigated. For cylinders and spheres, a size-driven phase transition occurs and the dielectric susceptibility is always enhanced at small size. However for films, whether there is a size-phase transition depends on the surface ferroelectricity. Our calculations are in qualitative agreement with measurements on barium titanate and lead titanate.

Ferroelectric diffuse phase transitions and dielectric susceptibility dispersion in the Landau-Ginzburg model with regard to fluctuations

Abstract Complex dielectric susceptibility of ferroelectrics as a function of parameters characterizing the system structure is calculated within the Landau-Ginzburg model using the Fokker-Planck kinetic equation. The formal solution is represented as a path integral, calculated by original techniques accounting for fluctuations. Results obtained allow to explain qualitatively diffuse phase transition in relaxor ferroelectrics as well as the spontaneous transition from relaxor type to first-order phase transition. Experimental investigation of PUT x/65/35 ceramics at intermediate La concentration x (6-7 at.%) show qualitative agreement with calculations.

Modified Lumped Parameter Method for Measurements of Dielectric Susceptibility in Ferroelectrics

The transmission techniques for dielectric measurements can be classified into two categories; one belongs to the lumped capacitance method and the other is related to the distributed parameter method. In reality, however, the dielectric dispersion for high dielectric constant materials in the frequency range 1 MHz–5 GHz could not be made accurately by using the transmission techniques. In this work, a modified lumped parameter method has been discussed. We call this modified method as the quasi lumped parameter method which is especially suitable for the microwave measurements of dielectric dispersion for high dielectric materials in a particular frequency region. The proposed method combines some features of both the lumped parameter method and the distributed parameter method. By using this measurement method, the measurements of dielectric dispersions are presented for several ferroelectric materals, such as Pb(Zr1-x Tix )O3, and BaTiO3 in the frequency domain from 1 MHz to 1 GHz.

Influence of the dielectric constant anisotropy on the poling of ferroelectrics

Abstract By calculating the potential distribution in ferroelectric crystals with applied electric field it is shown that—depending on the domain geometry—large field distortions occur which are due to the anisotropy of the dielectric susceptibility in ferroelectrics. These distortions can explain many of the problems showing up when poling crystals by an electric field.

Paraelectric large signal susceptibility of ferroelectrics with Gaussian distribution of relaxation times

Paraelectric large signal susceptibility of ferroelectrics with Gaussian distribution of relaxation times