M. Marvan

Patterning of dielectric nanoparticles using dielectrophoretic forces generated by ferroelectric polydomain films

A theoretical study of a dielectrophoretic force, i.e., the force acting on an electrically neutral particle in the inhomogeneous electric field, which is produced by a ferroelectric domain pattern, is presented. It has been shown by several researchers that artificially prepared domain patterns with given geometry in ferroelectric single crystals represent an easy and flexible method for patterning dielectric nanoobjects using dielectrophoretic forces. The source of the dielectrophoretic force is a strong and highly inhomogeneous (stray) electric field, which exists in the vicinity of the ferroelectric domain walls at the surface of the ferroelectric film. We analyzed dielectrophoretic forces in the model of a ferroelectric film of a given thickness with a lamellar 180° domain pattern. The analytical formula for the spatial distribution of the stray field in the ionic liquid above the top surface of the film is calculated including the effect of free charge screening. The spatial distribution of the diel...

Electrocaloric effect as a cause of dielectric loss

The difference between adiabatic and isothermal susceptibilities is caused by electrocaloric effect. Here we show how this effect contributes to dielectric dispersion in a sample of finite dimensions or in a non-homogeneous material. Maximum contribution to dielectric losses occurs at a frequency that is inversely proportional to the square of characteristic dimension. The first Fourier components of susceptibility in a non-pyroelectric material are proportional to the square of the amplitude of ac field. In a pyroelectric material with temperature dependent susceptibility a contribution to static polarisation arises due to alternating electric field.

The electric polarization induced by temperature gradient and associated thermoelectric effects

It is shown that the possible existence of a direct effect, which consists in the production of electric polarization in a temperature gradient, is connected with the existence of effects that are analogous to the known thermoelectric effects. The thermoelectric effects under study play a role in a periodic regime of temperature and electric current.

Influence of electrocaloric effect upon the dynamic susceptibility of multi-domain ferroelectric materials

AbstractIn anti-parallel domains, the electrocaloric effect has opposite signs. At the dynamic measurement of susceptibility there exists a temperature field inside the crystal, which varies both in space and in time and which affects the measured susceptibility. The heat conduction results in dielectric losses, the maximum value of which almost equals one half of the difference of susceptibilities at constant temperatureϰT and at constant entropyϰS. The frequency, at which these losses reach the maximum value, is given by the formula

Pyroelectricity and compositionally graded ferroelectrics: a brief review of our theoretical approach

\omega _r = q \cdot \frac{{8\lambda }}{{\varrho c_E W^2 }}

Distributions of Electric and Elastic Fields at 90° Domain Boundaries in Ferroelectric Thin Layer—Various Configurations

whereq is a numerical factor, given by-the unequality 1·25<q<1·30,λ is the thermal conductivity,ϱ the density,cE is the specific heat, andW the width of the domains. In the vicinity of the frequencyωr, the real component of the susceptibility mostly differs from the extreme valuesϰT andϰS.

Electric polarization induced by strain gradient

Anomalous pyroelectric effect has been repeatedly observed in ferroelectric films which were compositionally graded or in which strain gradient or temperature gradient was realized. The effect is represented by the shift of the hysteresis P(E) loop center due to the change of temperature. Here we propose a new interpretation of this property. It is based on the assumption that the concentration gradient induces additional polarization. This is characterized by macroscopic description based on the modified Landau-Devonshire thermodynamic potential f(P). The graphical representation of this modified potential is an asymmetric double-well. The hysteresis phenomenon is described by the motion of the “representative Brown particle” in this double-well; the shape of the latter is modulated by the time-dependent electric field. The observed anomalous pyroelectric effect is based on the coherence of the asymmetry and kinetic aspect of the phenomenon.

Dielectrophoretic forces generated by ferroelectric polydomain films

In the last decade, the properties of compositionally graded ferroelectric films (CGFF) have become an essential and very often addressed research topic of ferroelectric materials. Many theoretical discussions of CGFF have been already presented, however there are several drawbacks. This is the summary of the main results of the authors: (a) it is essential that the classical Landau free energy density will be modified by an additional term of the γP grad c type (c is the composition ratio of different atoms), (b) the experimentally observed shift of hysteresis loop along the polarization axis must be necessarily described by a kinetic equation. Our approach is limited, being based on the assumption that CGFF is an ideally nonconductive material. In this article we compare our approach to the available theories which consider the CGFF to be a semiconductor.