arXiv subjects

E. A. Eliseev

Publications and source records attributed to E. A. Eliseev.

53 records · Page 3Linked to original sources

arXiv2008

Probing the role of single defects on the thermodynamics of electric-field induced phase transitions

The kinetics and thermodynamics of first order transitions is universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially-resolved imaging of a single defect center in multiferroic BiFeO3 thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially-resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.

cond-mat.mtrl-sci↗

arXiv2007

Giant magnetoelectric effect induced by intrinsic surface stress in ferroic nanorods

The general approach for the consideration of the magnetoelectric effects in ferroic nanorods is proposed in the framework of the phenomenological theory. The intrinsic surface stress, magneto- and electrostriction as well as piezoelectric and piezomagnetic effects are included into the free energy. The intrinsic surface stress under the curved nanoparticle surface is shown to play an important role in the shift of ferroelectric and ferromagnetic transition temperatures and built-in magnetic and electric fields appearance, which are inversely proportional to the nanorod radius. We consider the case of quadratic and linear magnetoelectric coupling coefficients. The linear coupling coefficient is radius independent, whereas the quadratic ones include terms inversely proportional to the nanorod radius and thus strongly increase with decrease of the radius. The predicted giant relative dielectric tunability in the vicinity of ferromagnetic and ferroelectric phase transition points induced by quadratic magnetoelectric coupling increases by 2-50 times. The quadratic magnetoelectric coupling dramatically changes the phase diagrams of ferroic nanorods when the radius decreases. In particular the second order phase transition may become a first one, the triple point state characterized by continuous set of order parameters appears at zero external electric and magnetic fields and the tricritical points appear under external fields.

cond-mat.mtrl-sci↗

arXiv2006

Ferroelectricity enhancement in ferroelectric nanotubes

In this paper we study the size effects of the ferroelectric nanotube phase diagrams and polar properties allowing for effective surface tension and depolarization field influence. The approximate analytical expression for the paraelectric-ferroelectric transition temperature dependence on the radii of nanotube, polarization gradient coefficient, extrapolation length, surface tension and electrostriction coefficient was derived. It was shown that the transition temperature could be higher than the one of the bulk material for negative electrostriction coefficient. Therefore we predict conservation and enhancement of polarization in long ferroelectric nanotubes. Obtained results explain the observed ferroelectricity conservation and enhancement in Pb(Zr,Ti)O_3 and BaTiO_3 nanotubes.

cond-mat.mtrl-sci↗

arXiv2006

Anti-Ferroelectric Thin Films Phase Diagrams

In the paper we consider size effects of phase transitions and polar properties of the thin antiferroelectric films. We modified phenomenological approach proposed by Kittel. The Euler-Lagrange equations were solved by direct variational method. The free energy with renormalized coefficients depending on the film thickness has been derived. The approximate analytical expression for the coefficients dependence on film thickness, temperature, polarization gradient coefficient and extrapolation lengths were obtained. We have shown how the anti-ferroelectric double hysteresis loop transforms into the ferroelectric single one under the film thickness decrease. Proposed theoretical consideration explains the experimental results obtained in antiferroelectric PbZrO_3 thin films.

cond-mat.mtrl-sci↗

arXiv2006

Theoretical Description of Ferroelectric and Pyroelectric Hysteresis in the Disordered Ferroelectric-Semiconductor Films

We have modified Landau-Khalatnikov approach and shown that both the polar lattice and the screened charged defects determine the response of disordered ferroelectric-semiconductors. This system exhibits the spatially inhomogeneous switching under the external field while Landau-Khalatnikov model describes homogeneous switching with the sharp pyroelectric coefficient peak near the thermodynamic coercive field value. Our model gives more realistic pyroelectric hysteresis loop shape without any peaks near the coercive field and describes both qualitatively and quantitatively typical Pb(Zr,Ti)O_3 and (Sr,Ba)Nb_2O_6 films pyroelectric hysteresis loops.

cond-mat.mtrl-sci↗

arXiv2005

Modelling of Pyroelectric Response in Inhomogeneous Ferroelectric-Semiconductor Films

We have modified Landau-Khalatnikov approach and shown that the pyroelectric response of inhomogeneous ferroelectric-semiconductor films can be described by using six coupled equations for six order parameters: average displacement, its mean-square fluctuation and correlation with charge defects density fluctuations, average pyroelectric coefficient, its fluctuation and correlation with charge defects density fluctuations. Coupled equations demonstrate the inhomogeneous reversal of pyroelectric response in contrast to the equations of Landau-Khalatnikov type, which describe the homogeneous reversal with the sharp pyroelectric coefficient peak near the thermodynamic coercive field value. Within the framework of our model pyroelectric hysteresis loop becomes much smoother, thinner and lower as well as pyroelectric coefficient peaks near the coercive field completely disappear under the increase of disordering caused by defects. This effect is similar to the well-known "square to slim transition" of the ferroelectric hysteresis loops in relaxor ferroelectrics. Also the increase of defect concentration leads to the drastic decrease of the coercive field typical for disordered ferroelectrics. Usually pyroelectric hysteresis loops of doped and inhomogeneous ferroelectrics have typical smooth shape without any pyroelectric coefficient peaks and coercive field values much lower than the thermodynamic one. Therefore our approach qualitatively explains available experimental results. Rather well quantitative agreement between our modelling and typical Pb(Zr,Ti)O3-film pyroelectric and ferroelectric loops has been obtained.

cond-mat.mtrl-sci↗

arXiv2005

Theory of the size effect of the properties of the relaxor ferroelectric films

For the first time we proposed the model for the calculations of the relaxor ferroelectrics films properties in the framework of the random field theory. We took into account the misfit strain between film and substrate as well as surface piezoelectric effect that causes built-in electric field in the strained films. In the statistical theory framework we calculated random field distribution function with the electric dipoles and monopoles as the field sources. It was shown that with thickness decrease the mean field decreases, while the width of the distribution function increases. This leads to the additional smearing of the phase transition in the films in comparison to the bulk relaxors. As an example the dependence of the order parameter and dielectric susceptibility on the film thickness, temperature and random fields distribution function parameters was obtained. For free standing film the existence of critical thickness of relaxor state transformation into glassy state was predicted. Contrary to this the appearance of misfit strain induced ferroelectric phase appeared to be possible for some pairs film-substrate. We have shown that susceptibility temperature maximum shift with frequency in relaxor ferroelectric thin films obeys Vogel-Fulcher law with parameters dependent on film thickness. For the first time the analytical dependences of freezing temperature decreases and activation energy on the thickness was obtained, namely freezing temperature decreases and activation energy increases with film thickness decrease. Obtained results quantitatively agree with the available experimental data for PbMg1/3Nb2/3O3 relaxor thin films.

cond-mat.mtrl-sci↗

arXiv2005

Ferroelectric thin films phase diagrams with self-polarized phase and electret state

In present work we calculated the three components of polarization in phenomenological theory framework by consideration of three Euler-Lagrange equations, which include mismatch effect and influence of misfit dislocations, surface piezoelectric effect caused by broken symmetry on the film surface, surface tension and depolarization field. These equations were solved with the help of variational method proposed by us earlier. This approach lead to the free energy in the form of algebraic equation of different powers of polarization components with the coefficients dependent on film thickness, mismatch effect, temperature and other parameters. Several new terms proportional to misfit strain appeared in the free energy expression: built-in electric field normal to the surface originated from piezoelectricity in vicinity of surface even for the cubic symmetry of bulk ferroelectrics, odd powers of normal to the surface component of polarization. The obtained free energy made it possible to calculate all properties of the film by conventional procedure of minimization. As an example we calculated phase diagrams of PZT 50/50 films on different substrates that lead to compressive or tensile strain. The calculations of pyroelectric coefficient and dielectric permittivity temperature dependencies had shown the electret-like polar state, e.g. existence of pyroelectricity, below the critical thickness of ferroelectric-paraelectric phase transitions. Our theory predicts, that mismatch-induced field could be compatible with thermodynamic coercive field and thus cause self-polarization in thin ferroelectric films.

cond-mat.soft↗

arXiv2004

Distribution function of the random field and polar properties of the relaxor ferroelectric films

The model for calculation of relaxor ferroelectrics thin films properties is proposed. The basis of the model is the theory of random field. This field is originated from the chemical disorder allowing for influence of the film surfaces, which destroys the polar long-range order and transform it into mixed state of ferroelectric glass (FG) or dipole glass (DG). The spatial profiles and averaged over coordinate inside the film values of properties of relaxor ferroelectric film were calculated with the random field distribution function. As an example the dependence of the order parameter on film thickness, temperature and distribution function characteristics was obtained. The critical thickness and temperature of the size-driven phase transition from FG to DG state as a function of the film and distribution function characteristics were calculated.

cond-mat.mtrl-sci↗

arXiv2004

Size effects in the thin films of order - disorder ferroelectrics subject to the depolarization field

The films of order-disorder type ferroelectrics were considered in the mean field approximation taking into account depolarization field. It was shown that size effects in this system could be described on the base of bulk system equation of state with Curie temperature dependent on the film thickness. The critical size hc and critical temperature Tc of phase transition from ferroelectric to paraelectric phase was calculated allowing for the depolarization field contribution. The comparison of the polarization dependence on the film thickness, temperature and electric field for the films of order-disorder and displacement type ferroelectrics is performed. In particular it was shown that all the dipoles become ordered at T=0 independently on the film thickness for h>hc contrary to the displacement type ferroelectrics. Critical thickness appeared larger and polarization distribution sharper for the displacement type ferroelectrics than for order-disorder type ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2004

Comparative study of pyroelectric response of PZT-film/Si, PZT-film/Por-Si/Si and PVDF-film/Si structures

The comparative investigation of pyroelectric response modulation frequency dependences of structures of "polar active film-Si substrate" type based on PZT and PVDF and of structures of "polar active film - buffer layer - Si substrate" type based on PZT and porous silicon (por-Si) has been carried out. By photopyroelectric modulation method the thermowave pyroelectric "under-surface" probing was performed and amplitude-to-frequency and phase-to-frequency dependences of pyroelectric response of investigated systems in the voltage and current modes were obtained. By performing the analysis of obtained dependences the thermal diffusivity values of investigated PZT and PVDF films, and also por-Si interlayer were estimated. The results of theoretical consideration of the structures under investigation are in a good agreement with the experimental data. The problem of thermal decoupling and self-decoupling from position of chain "frequency-thickness-material" and question of complete and incomplete thermal linkage are briefly discussed. The obtained results show that a por-Si layer is a suitable material for effective thermal decoupling of polar active film and heat removing Si-substrate which realized in significant increase of pyroelectric response value and approach it to that of characteristic for a free sensitive element.

cond-mat.mtrl-sci↗

arXiv2002

Ferroelectric thin films properties: depolarization field and Landau free-energy coefficients renormalization

The calculation of the polarization in ferroelectric thin films is performed using an analytical solution of the Euler-Lagrange differential equation with boundary conditions with different extrapolation lengths of positive sign on the surfaces. The depolarization field effect is taken into account in the model for a short-circuited single domain film, that is a perfect insulator. It is shown that the calculation of the polarization and other properties profiles and average values can be reduced to the minimization of the free energy expressed as a power series of the average polarization with a renormalized coefficient which depends on temperature, film thickness, extrapolation lengths, and a coefficient for the polarization gradient term in the free energy functional, the depolarization field being also included into the renormalized coefficient. The function defining the space distribution properties is calculated as well and its amplitude is shown to coincide with the average polarization. The detailed calculations of the spontaneous polarization, dielectric susceptibility and pyrocoefficient is performed. The divergence of the dielectric susceptibility and pyrocoefficient for critical parameters of the thickness induced ferroelectric phase transition, namely at temperature T(cl) and critical length l(c), is shown to exist with and without the depolarization field contribution, although the values of T(cl) and l(c) are different in both cases. The detailed analysis of the depolarization field space distribution and of this field dependence on temperature and film thickness is performed.

cond-mat.mtrl-sci↗

arXiv2001

Size effects of pyroelectric coefficient and dielectric susceptibility in ferroelectric thin films

We calculate the pyrocoefficient, static dielectric susceptibility profiles and its thickness dependence of ferroelectric thin films. Also, the temperature dependences of above quantities have been calculated. For the calculations we use Landau phenomenological theory, leading to Lame equations. These equations subject to boundary conditions with different extrapolation length on the surfaces have been solved numerically. The divergency of pyroelectric coefficient and static dielectric susceptibility in the vicinity of thickness induced ferroelectric phase transition (i.e. at $l\approx l_c$ or $% T\approx T_{cl}$) has been shown to be the most prominent size effect in ferroelectric thin films.

cond-mat.mtrl-sci↗

arXiv2000

Random field based model of mixed ferroelectrics phase diagram

The equations for phase transitions temperatures, order parameters and critical concentrations of components have been derived for mixed ferroelectrics. The electric dipoles randomly distributed over the system were considered as a random field sources. We derive a random field distribution function for different orientations of the electric dipoles with nonlinear and spatial correlation effects included.

cond-mat.mtrl-sci↗

arXiv2000

Phase diagram of mixed system of ferroelectric relaxors in the random field theory framework

We suggest a random field based model for calculation of physical properties of mixed ferroelectric relaxors. Our model naturally incorporates the different orientations of electric dipoles (related to different solid solution components) as well as the contribution of nonlinear and correlation effects of random field. We calculate the transition temperature $T_c$ as well as concentrational and temperature dependence of order parameters.

cond-mat.mtrl-sci↗

arXiv2000

Static and dynamic properties of ferroelectric thin film multilayers

A thermodynamic theory of ferroelectric thin film multilayers is developed. The free energy function is written down using a multilayer model in which c-domain layers of one ferroelectric material alternate with a-domain layers of a second ferroelectric material. We assume that the interfaces are perfectly sharp and that the polarization at these boundaries is zero. The renormalization of the free energy coefficients due to the stresses in the films and to the depolarizing field was taken into account, as well as the renormalization of the coefficients of the polarization gradients. The equilibrium inhomogeneous polarization temperature and its thickness dependence were determined from the solutions of the Euler-Lagrange equations resulting from the minimization of the free energy functional. A thickness induced ferroelectric phase transition is shown to exist and its transition temperature and critical layer thickness depend on the domain orientation. The criteria for ''a/c'', ''c/c'' and ''a/a'' domain multilayering are calculated and expressed via coefficients of the free energy density and the layer thickness. The calculated multilayer susceptibility diverges at the transition temperature of the thickness induced ferroelectric phase. This divergence is shown to be the origin of the giant dielectric response observed in some multilayers. The theory gives an excellent fit to the temperature dependence of the giant susceptibility observed recently in multilayers of PbTiO$_{3}$-Pb$_{1-x}$La$_{x}$TiO$_{3}$ ($x=0.28$).

cond-mat.mtrl-sci↗

arXiv1998

Hadron Probing of the Deuteron Structure at Short Distances in Deuteron Breakup Reactions

We discuss deuteron $A(d,p)X$ breakup and cumulative pion production $A(d,π)X$ in the framework of constituent quark model of the deuteron. We demonstrate that consideration of the Pauli principle at the quark level, as well as multiple scattering, affect drastically cross section and polarization observables of these reactions and provide good description of the experimental data.

nucl-th↗