arXiv subjects

Eugene A. Eliseev

Publications and source records attributed to Eugene A. Eliseev.

At least 145 records · Page 8Linked to original sources

arXiv2012

Anisotropic conductivity of uncharged domain walls in BiFeO3

Experimental observations suggest that nominally uncharged, as-grown domain walls in ferroelectric thin films can be conductive, yet comprehensive theoretical models to explain this behavior are lacking. Here, Landau theory is used to evolve an analytical treatment of the anisotropic carrier accumulation by nominally uncharged domain walls in multiferroic BiFeO3. Strong angular dependence of the carrier accumulation by 180-degree domain walls originates from local band bending via angle-dependent electrostriction and flexoelectric coupling mechanisms. Theoretical results are in qualitative agreement with experimental data, and provide a Landau-Ginzburg-Devonshire counterpart that is consistent with recent first principles calculations. These studies suggest that a significantly more diverse range of domain wall structures could possess novel electronic properties than previously believed. Similarly, emergent electronic behaviors at ferroic walls are typically underpinned by multiple mechanisms, necessitating first-principle studies of corresponding coupling parameters.

cond-mat.mtrl-sci↗

arXiv2012

Conductivity of twin walls - surface junctions in ferroelastics: interplay of deformation potential, octahedral rotations, improper ferroelectricity and flexoelectric coupling

Electronic and structural phenomena at the twin domain wall-surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin walls - surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin walls static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric and rotostriction coupling leads to the appearance of the improper polarization and electric fields proportional to the structural order parameter gradient in the vicinity of the twin walls - surface junctions. The "flexo-roto" fields leading to the carrier accumulation are considered as indirect mechanism of the twin walls conductivity. Comparison of the direct and indirect mechanisms illustrates complex range of phenomena directly responsible for domain walls static conductivity in materials with multiple order parameters.

cond-mat.mtrl-sci↗

arXiv2012

Ionically-mediated electromechanical hysteresis in transition metal oxides

Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order GLD expansion coefficient, rendering material effectively ferroelectric. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

cond-mat.mtrl-sci↗

arXiv2012

Mesoscopic mechanism of the domain wall interaction with elastic defects in ferroelectrics

The role of elastic defects on the kinetics of 180-degree uncharged ferroelectric domain wall motion is explored using continuum time-dependent LGD equation with elastic dipole coupling. In one dimensional case, ripples, steps and oscillations of the domain wall velocity appear due to the wall-defect interactions. While the defects do not affect the limiting-wall velocity vs. field dependence, they result in the minimal threshold field required to activate the wall motions. The analytical expressions for the threshold field are derived and the latter is shown to be much smaller than the thermodynamic coercive field. The threshold field is linearly proportional to the concentration of defects and non-monotonically depends on the average distance between them. The obtained results provide the insight into the mesoscopic mechanism of the domain wall pinning by elastic defects in ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2011

Interfacial Polarization and Pyroelectricity in Antiferrodistortive Structures Induced by a Flexoelectric Effect and Rotostriction

Theoretical analysis based on the Landau-Ginzburg-Devonshire (LGD) theory is used to show that the product effect of flexoelectricity and rotostriction can lead to a spontaneous polarization in the vicinity of antiphase boundaries, ferroelastic twin walls, surfaces and interfaces in the octahedrally tilted phase of otherwise non-ferroelectric perovskites such as CaTiO3, SrTiO3, and EuTiO3. As an example, we numerically demonstrate a large spontaneous polarization on the order of 1-5muC/cm2 at the SrTiO3 antidistortive phase boundaries at temperatures lower than the antiferrodistortive structural phase transition temperature of ~105 K

cond-mat.mtrl-sci↗

arXiv2011

Domain wall conduction in multiaxial ferroelectrics

The conductance of domain wall structures consisting of either stripes or cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed. The effects of the domain size, wall tilt and curvature, on charge accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory for polarization combined with Poisson equation for charge distributions. Both the classical ferroelectric parameters including expansion coefficients in 2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling, inhomogeneous elastic strains and electrostriction are included in the present analysis. Spatial distributions of the ionized donors, free electrons and holes were found self-consistently using the effective mass approximation for the respective densities of states. The proximity and size effect of the electron and donor accumulation/depletion by thin stripe domains and cylindrical nanodomains are revealed. In contrast to thick domain stripes and thicker cylindrical domains, in which the carrier accumulation (and so the static conductivity) sharply increases at the domain walls only, small nanodomains of radius less then 5-10 correlation length appeared conducting across entire cross-section. Implications of such conductive nanosized channels may be promising for nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2011

Ferroelectricity and ferromagnetism in EuTiO3 nanowires

We predicted the ferroelectric-ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first principles calculations. Since bulk EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the possibility of inducing the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk to nanosystems. Our results indicate that ferroelectric spontaneous polarization of ~0.1-0.5C/m2 is induced in EuTiO3 nanowires due to the intrinsic surface stress, which is inversely proportional to the nanowire radius. The spontaneous polarization exists at temperatures lower than 300 K, for the wire radius less than 1 nm and typical surface stress coefficients ~ 15 N/m. Due to the strong biquadratic magnetoelectric coupling, the spontaneous polarization in turn induces the ferromagnetic phase at temperatures lower than 30 K for 2 nm nanowire, and at temperatures lower than 10 K for 4 nm nanowire in EuTiO3. Thus we predicted that the EuTiO3 nanowires can be the new ferroelectric-ferromagnetic multiferroic.

cond-mat.mtrl-sci↗

arXiv2010

Complete symmetry analyses of the surface-induced piezomagnetic, piezoelectric and linear magnetoelectric effects

The impact of the surface on the magnetic symmetry is studied. It is shown how symmetry breaking transforms the "seeding" 90 bulk magnetic classes, which include 66 piezomagnetic classes and 58 magnetoelectric classes, into the 21 surface-induced magnetic classes, which all are piezomagnetic, piezoelectric and 19 of them are linear magnetoelectric. So, the new piezomagnetic, piezoelectric properties and linear magnetoelectric coupling should appear in nanomaterials, which are absent in the bulk.

cond-mat.mtrl-sci↗

arXiv2009

Phase diagrams and polar properties of ferroelectric nanotubes and nanowires

In this paper we study the size effects of the ferroelectric nanotube and nanowire phase diagrams and polar properties allowing for radial stress 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, radial stress (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 and small depolarization field. Therefore we predict conservation and enhancement of polar properties in long cylindrical ferroelectric nanoparticles. Obtained results explain the observed ferroelectricity conservation and enhancement in Pb(Zr,Ti)O_3 and BaTiO_3 nanowires and nanotubes. Moreover, despite made assumptions and approximations our modelling appeared in a surprisingly good agreement with observed ferroelectric and local piezoresponse hysteresis loops.

cond-mat.mtrl-sci↗

arXiv2009

Spontaneous flexoeffect in nanoferroics

Within the Landau-Ginsburg-Devonshire phenomenological approach we study the ferroic nanosystems properties changes caused by the flexo-effect (flexoelectric, flexomagnetic, flexoelastic) existing spontaneously due to the inhomogeneity of order parameters. Exact solution for the spatially inhomogeneous mechanical displacement vector allowing for flexo-coupling contribution was found for nanowires and thin pills. Strong influence of flexo-effect in nanorods and thin pills leads to the displacements of the atoms resulting into the unit cell symmetry changes, which lead to the phase transition temperature shift, as well as the flat geometry in radial direction transforms into the saucer-like one. The new phenomena can be considered as true manifestation of the spontaneous flexo-effect existence. It was shown that flexo-effect leads to (a) the appearance of new linear and nonlinear contribution and renormalization of coefficients before the order parameter gradient, (b) essentially influences the transition temperature, piezoelectric response and the spatial distribution of the order parameter, (c) results in renormalization of extrapolation length in the boundary conditions.

cond-mat.mtrl-sci↗

arXiv2008

Thermodynamics of nanodomain formation and breakdown in Scanning Probe Microscopy: Landau-Ginzburg-Devonshire approach

Thermodynamics of tip-induced nanodomain formation in scanning probe microscopy of ferroelectric films and crystals is studied using the Landau-Ginzburg-Devonshire phenomenological approach. The local redistribution of polarization induced by the biased probe apex is analyzed including the effects of polarization gradients, field dependence of dielectric properties, intrinsic domain wall width, and film thickness. The polarization distribution inside subcritical nucleus of the domain preceding the nucleation event is very smooth and localized below the probe, and the electrostatic field distribution is dominated by the tip. In contrast, polarization distribution inside the stable domain is rectangular-like, and the associated electrostatic fields clearly illustrate the presence of tip-induced and depolarization field components. The calculated coercive biases of domain formation are in a good agreement with available experimental results for typical ferroelectric materials. The microscopic origin of the observed domain tip elongation in the region where the probe electric field is much smaller than the intrinsic coercive field is the positive depolarization field in front of the moving counter domain wall. For infinitely thin domain walls local domain breakdown through the sample depth appears. The results obtained here are complementary to the Landauer-Molotskii energetic approach.

cond-mat.mtrl-sci↗

arXiv2008

Built-in surface field effect on the 180-degree domain wall structure in ferroics

We consider the influence of the built-in surface field on the 180-degree domain wall profile in primary ferroics within Landau-Ginsburg-Devonshire phenomenological approach. We predict the effect of domain wall bending near the surface caused by the built-in field and derived corresponding approximate analytical expressions. At that the higher is the surface energy contribution (i.e. the smaller is corresponding extrapolation length) and/or the higher is the field, the stronger is the bending effect. Built-in surface field is one of the possible mechanisms of domain wall near surface broadening recently observed in the ferroics.

cond-mat.mtrl-sci↗

arXiv2008

The Interaction of an 180 degree Ferroelectric Domain Wall with a Biased Scanning Probe Microscopy Tip: Effective Wall Geometry and Thermodynamics in Ginzburg-Landau-Devonshire Theory

The interaction of ferroelectric 180 degree domain wall with a strongly inhomogeneous electric field of biased Scanning Probe Microscope tip is analyzed within continuous Landau-Ginzburg-Devonshire theory. Equilibrium shape of the initially flat domain wall boundary bends, attracts or repulses from the probe apex, depending on the sign and value of the applied bias. For large tip-wall separations, the probe-induced domain nucleation is possible. The approximate analytical expressions for the polarization distribution are derived using direct variational method. The expressions provide insight how the equilibrium polarization distribution depends on the wall finite-width, correlation and depolarization effects, electrostatic potential distribution of the probe and ferroelectric material parameters.

cond-mat.mtrl-sci↗

arXiv2008

Threshold fields for antiparallel ferroelectric domain wall motion

While an ideal antiparallel ferroelectric wall is considered a unit cell in width (~0.5nm), we show using phase field modeling that the threshold field for moving this wall dramatically drops by 2-3 orders of magnitude if the wall were diffuse by only ~2-3nm. Since antiparallel domain walls are symmetry allowed in all ferroelectrics, and since domain wall broadening on nanometer scale is widely reported in literature, this mechanism is generally applicable to all ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2008

Surface Effect on Domain Wall Width in Ferroelectrics

We study the effect of depolarization field related with inhomogeneous polarization distribution, strain and surface energy parameters on a domain wall profile near the surface of a ferroelectric film within the framework of Landau-Ginzburg-Devonshire phenomenology. Both inhomogeneous elastic stress and positive surface energy lead to the wall broadening at electrically screened surface. For ferroelectrics with weak piezoelectric coupling, the extrapolation length that defines surface energy parameter, affects the wall broadening more strongly than inhomogeneous elastic stress. Unexpectedly, the domain wall profile follows a long-range power law when approaching the surface, while it saturates exponentially in the bulk. In materials with high piezoelectric coupling and negligibly small surface energy (i.e. high extrapolation length) inhomogeneous elastic stress effect dominates.

cond-mat.mtrl-sci↗

arXiv2008

Quantitative piezoelectric force microscopy: Influence of tip shape, size, and contact geometry on the nanoscale resolution of an antiparallel ferroelectric domain wall

The structure of a single antiparallel ferroelectric domain wall in LiNbO3 is quantitatively mapped by piezoelectric force microscopy (PFM) with calibrated probe geometry. The PFM measurements are performed for 49 probes with the radius varying from 10 to 300 nm. The magnitude and variation of the experimental piezoelectric coefficient across a domain wall matches the profiles calculated from a comprehensive analytical theory, as well as 3-dimensional finite element method simulations. Quantitative agreement between experimental and theoretical profile widths is obtained only when a finite disk-type tip radius that is in true contact with the sample surface is considered, which is in agreement with scanning electron microscopy images of the actual tips after imaging. The magnitude of the piezoelectric coefficient is shown to be independent of the tip radius, and the PFM profile width is linearly proportional to the tip radius. Finally we demonstrate a method to extract any intrinsic material broadening of the ferroelectric wall width. Surprisingly wide wall widths of 20- 200nm are observed.

cond-mat.mtrl-sci↗

arXiv2008

Effect of the Intrinsic Width on the Piezoelectric Force Microscopy of a Single Ferroelectric Domain Wall

Intrinsic domain wall width is a fundamental parameter that reflects bulk ferroelectric properties and governs the performance of ferroelectric memory devices. We present closed-form analytical expressions for vertical and lateral piezoelectric force microscopy (PFM) profiles for the conical and disc models of the tip, beyond point charge and sphere approximations. The analysis takes into account the finite intrinsic width of the domain wall, and dielectric anisotropy of the material. These analytical expressions provide insight into the mechanisms of PFM image formation and can be used for quantitative analysis of the PFM domain wall profiles. PFM profile of a realistic domain wall is shown to be the convolution of its intrinsic profile and resolution function of PFM.

cond-mat.mtrl-sci↗

arXiv2008

Imaging Mechanism of Piezoresponse Force Microscopy in Capacitor Structures

The image formation mechanism in Piezoresponse Force Microscopy (PFM) of capacitor structures is analyzed. We demonstrate that the spatial resolution is a bilinear function of film and top electrode thicknesses, and derive the corresponding analytical expressions. For many perovskites, the opposite contributions of d31 and d33 components can result in anomalous domain wall profiles. This analysis establishes the applicability limits of PFM for polarization dynamics studies in capacitors, and applies to other structural probes, including focused X-ray studies of capacitor structures.

cond-mat.mtrl-sci↗