arXiv subjects

Maya D. Glinchuk

Publications and source records attributed to Maya D. Glinchuk.

At least 19 recordsLinked to original sources

arXiv2023

Phase transitions in ferroelectric domain walls

Despite multiple efforts, there exist many unsolved fundamental problems related with detection and analysis of internal polarization structure and related phase transitions in ferroelectric domain walls. Their solution can be very important for the progress in domain wall nanoelectronics and related applications in advanced memories and other information technologies. Here, we theoretically study the features of phase transitions in the domain walls, which are potentially detectable by the scanning probe capacitance microwave microscopy. The finite element modelling based on the Landau-Ginzburg-Devonshire theory is performed for the capacitance changes related with the domain wall motion in a multiaxial ferroelectric BaTiO$_3$.

cond-mat.mtrl-sci↗

arXiv2021

A Combined Theoretical and Experimental Study of the Phase Coexistence and Morphotropic Boundaries in Ferroelectric-Antiferroelectric-Antiferrodistortive Multiferroics

The physical nature of the ferroelectric (FE), ferrielectric (FEI) and antiferroelectric (AFE) phases, their coexistence and spatial distributions underpin the functionality of antiferrodistortive (AFD) multiferroics in the vicinity of morphotropic phase transitions. Using Landau-Ginzburg-Devonshire (LGD) phenomenology and a semi-microscopic four sublattice model (FSM), we explore the behavior of different AFE, FEI and FE long-range orderings and their coexistence at the morphotropic phase boundaries in FE-AFE-AFD multiferroics. These theoretical predictions are compared with the experimental observations for dense Bi1-yRyFeO3 ceramics, where R is Sm or La atoms with the fraction 0 < y< 0.25, as confirmed by the X-ray diffraction (XRD) and Piezoresponse Force Microscopy (PFM). These complementary measurements were used to study the macroscopic and nanoscopic transformation of the crystal structure with the doping. The comparison of the measured and calculated AFE/FE phase fractions demonstrate that the LGD-FSM approach well describes the experimental results obtained by XRD and PFM for Bi1-yRyFeO3. Hence, this combined theoretical and experimental approach provides further insight into the origin of the morphotropic boundaries and coexisting FE and AFE states in model rare-earth doped multiferroics.

cond-mat.mtrl-sci↗

arXiv2020

Correlation between corrugation-induced flexoelectric polarization and conductivity of low-dimensional transition metal dichalcogenides

Tunability of polar and semiconducting properties of low-dimensional transition metal dichalcogenides (TMDs) have propelled them to the forefront of fundamental and applied physical research. These materials can vary from non-polar to ferroelectric, and from direct-band semiconductor to metallic. However, in addition to classical controls such as composition, doping, and field effect in TMDs the additional degrees of freedom emerge due to the curvature-induced electron redistribution and associated changes in electronic properties. Here we numerically explore the elastic and electric fields, flexoelectric polarization and free charge density for a TMD nanoflake placed on a rough substrate with a sinusoidal profile of the corrugation using finite element modelling. Numerical results for different flake thickness and corrugation depth yield insight into the flexoelectric nature of the out-of-plane electric polarization and establish the unambiguous correlation between the polarization and static conductivity modulation caused by inhomogeneous elastic strains coupled with deformation potential and strain gradients, which evolve in TMD nanoflake due to the adhesion between the flake surface and corrugated substrate. We revealed a pronounced maximum at the thickness dependences of the electron and hole conductivity of MoS2 and MoTe2 nanoflakes placed on a metallic substrate, which opens the way for their geometry optimization towards significant improvement their polar and electronic properties, necessary for their advanced applications in nanoelectronics and memory devices.Specifically, obtained results can be useful for elaboration of nanoscale straintronic devices based on the bended MoS2, MoTe2 and MoSTe nanoflakes, such as diodes and bipolar transistors with a bending-controllable sharpness of p-n junctions.

cond-mat.mtrl-sci↗

arXiv2020

Flexo-induced ferroelectricity in low dimensional transition metal dichalcogenides

We developed a Landau type theory for the description of polar phenomena in low-dimensional transition metal dichalcogenides (TMDs), specifically exploring flexoelectric origin of the polarization induced by a spontaneous bending and by inversion symmetry breaking due to the interactions with substrate. We consider the appearance of the spontaneous out-of-plane polarization due to the flexoelectric coupling with the strain gradient of the spontaneous surface rippling and surface-induced piezoelectricity. Performed calculations proved that the out-of-plane spontaneous polarization, originated from flexoelectric effect in a rippled TMD, is bistable and reversible by a non-uniform electric field. In contrast, the spontaneous polarization induced by a misfit strain and symmetry-sensitive surface-induced piezoelectric coupling, cannot be reversed by an external electric field. The special attention is paid to the spectral analysis of the linear dielectric susceptibility and gain factor, which enhancement is critically important for the observation of the polar phenomena in low-dimensional TMDs by the surface-enhanced vibrational spectroscopy.

cond-mat.mtrl-sci↗

arXiv2019

Analytical description of the size effect on pyroelectric and electrocaloric properties of ferroelectric nanoparticles

Using Landau-Ginzburg-Devonshire theory and effective medium approximation, we analytically calculate typical dependences of the pyroelectric and electrocaloric coefficients on external electric field, temperature and radius for spherical single-domain ferroelectric nanoparticles. The considered physical model corresponds to the nanocomposite with small fraction of ferroelectric nanoparticles. Within the framework of the analytical model we establish how the size changes determine the temperature and field behavior pyroelectric and electrocaloric coefficients on example of BaTiO3 nanoparticles covered by a semiconducting shell and placed in a dielectric polymer. We show that by changing the particle size one can induce maxima of the pyroelectric coefficient and electrocaloric temperature variation, control their width, height and sign. Obtained analytical expressions allow selecting the interval of particle sizes, voltage, and/or temperature for which pyroelectric energy conversion and electrocaloric coefficient are optimal for applications. The observed size effect opens the possibility to control pyroelectric and electrocaloric properties of ferroelectric nanocomposites that can be important for their advanced applications in energy convertors and cooling systems.

cond-mat.mtrl-sci↗

arXiv2018

Possible Electrochemical Origin of Ferroelectricity in HfO2 Thin Films

Recent observations of unusual ferroelectricity in thin films of HfO_2 and related materials have attracted broad interest to the materials and led to the emergence of a number of competing models for observed behaviors. Here we develop the electrochemical mechanism of observed ferroelectric-like behaviors, namely the collective phenomena of elastic and electric dipoles originated from oxygen vacancies formation in the vicinity of film surfaces, as well as from grain boundaries and other types of inhomogeneities inside the film. The ferroelectric phase is induced by the "electrochemical" coupling, that is the joint action of the omnipresent electrostriction and "chemical" pressure, which lead to the sign change of the positive coefficient alfa in the quadratic term alfa*P^2 in the order-disorder type thermodynamic functional depending on polarization P. Negative coefficient alfa becomes the driving force of the transition to the long-range ordered ferroelectric phase with the spontaneous polarization P in the direction normal to the film surface. Using the above ideas, we estimated that the reversible ferroelectric polarization, as high as (0.05 - 0.2) C/m^2, can be induced by oxygen vacancies in HfO_2 films of thickness less than (20 - 30) nm. Semi-quantitative agreement with available experimental data is demonstrated.

cond-mat.mtrl-sci↗

arXiv2018

Oxygen vacancies induced ferroelectricity in relaxors with ABO3 structure

The consideration of oxygen vacancies influence on the relaxors with perovskite structure was considered in the framework of Landau-Ginzburg-Devonshire phenomenological theory. The theory applicability for relaxors is based on the existence of some hidden soft phonon polar mode in them, and its frequency could be zero at some negative temperature TC*. Main attention was paid to PZN-PLZT relaxor described by formula 0.3Pb(Zn1/3Nb2/3)O3-0.7(Pb0.96La0.04(ZrxTi1-x)0.99O3) with x = 0.52, where earlier experimental investigation of oxygen vacancies influence on the polar properties was performed and the evidence of oxygen vacancies induced ferroelectricity was obtained. Since the oxygen vacancies are known to be elastic dipoles, they influence upon elastic and electric fields due to Vegard and flexoelectric coupling. We include the vacancies elastic and electrostrictive contribution into free energy functional. The calculations of the vacancies impact on polar properties were performed using their concentration distribution function. It was shown that the negative Curie temperature of a relaxor TC* is renormalized by the elastic dipoles due to the electrostrictive coupling and can become positive at some large enough concentration of the vacancies. We calculated the local polarization and electric field induced by the flexo-chemical coupling in dependence on the concentration of oxygen vacancies. The coexistence of FE phase and relaxor state can take place because of inhomogeneity of vacancies concentration distribution.

cond-mat.mtrl-sci↗

arXiv2018

Anomalies Of Phase Diagrams And Physical Properties Of Antiferrodistortive Perovskide Oxides

The influence of rotomagnetic (RM), rotoelectric (RE) and magnetoelectric (ME) coupling on phase diagram and properties of antiferrodistortive (AFD) perovskite oxides was reviewed. The main examples we consider in the review are typical AFD perovkites, such as incipient ferroelectrics EuTiO3, SrTiO3, EuxSr1-xTiO3, multiferroic BiFeO3 and Bi1-xRxFeO3 (x = La, Nd). The strong influence of RM, RE and ME couplings on the physical properties and phase diagrams including antiferromagnetic (AFM), ferroelectric (FE) and structural AFD phases has been revealed in the framework of Landau-Ginzburg-Devonshire (LGD) theory, as well as the prediction of novel (double and triple) multiferroic phases has been demonstrated. In the review we are especially focused on (a) the possibility to induce FM (FE) phase in EuTiO3 (as well as in other paraelectric AFM oxides) by the application of an electric (magnetic) field due to the ME coupling; (b) the analysis of the size effects and novel phases in EuxSr1-xTiO3 nanosystems, where the LGD predicts the presence of the triple AFD-FE-FM(AFM) phase at low temperatures; (c) the appearance of improper spontaneous polarization and pyroelectricity in the vicinity of antiphase domain boundaries, structural twin walls, surfaces and interphases in the AFD phase of non-ferroelectric SrTiO3 induced by the flexoelectricity and rotostriction; (d) the occurrence of low symmetry monoclinic phase with in-plane FE polarization in thin strained EuxSr1-xTiO3 films and its stabilization over wide temperature range by AFD oxygen octahedron tilts due to flexoelectric and rotostriction coupling; (e) discussion of a surprisingly strong size-induced increase of AFM transition temperature caused by the joint action of RM coupling with elastic stress accumulated in the intergrain spaces of BiFeO3 dense ceramics.

cond-mat.mtrl-sci↗

arXiv2018

Rotomagnetic coupling in fine grained multiferroic BiFeO3: Theory and experiment

Using Landau-Ginzburg-Devonshire (LGD) theory for BiFeO3 dense fine grained ceramics with quasi spherical grains and nanosized inter grain spaces enriched by elastic defects, we calculated a surprisingly strong size-induced increase of the AFM temperature caused by the joint action of rotomagnetic and magnetostrictive coupling. Notably that all parameters included in the LGD functional have been extracted from experiments, not assumed. Complementary we performed experiments for dense BiFeO3 ceramics, which revealed that the shift of antiferromagnetic transition to 690 K instead of 645 K for a single crystal. To explain theoretically the result, we consider the possibility to control antiferromagnetic state of multiferroic BiFeO3 via biquadratic antiferrodistortive rotomagnetic, rotoelectric, magnetostrictive and magnetoelectric couplings. According to our calculations the highest is the rotostriction contribution, the magnetostrictive and electrostriction contributions appeared smaller.

cond-mat.mtrl-sci↗

arXiv2017

Flexoelectricity induced spatially modulated phases in ferroics and liquid crystals (Author review)

In the review we briefly analyze the state-of-art in the theory of flexoelectric phenomena and analyze how significantly the flexoelectric coupling can change the polar order parameter distribution in different ferroics and liquid crystals. The special attention in paid to the appearance of the spatially modulated phases induced by the flexocoupling in condensed and soft matter. Results of theoretical modeling performed in the framework of the Landau-Ginzburg-Devonshire formalism revealed that the general feature, inherent to both ferroics and liquid crystals, is the appearance of the spatially-modulated phases is taking place with increasing of the flexocoupling strength. We'd like to underline that theoretical and experimental study of flexoelectricity and related phenomena in nanosized and bulk ferroics, liquid crystals and related materials are very important for their advanced applications in nanoelectronics, memory devices and LC displays.

cond-mat.mtrl-sci↗

arXiv2017

Defect driven flexo-chemical coupling in thin ferroelectric films

Using Landau-Ginzburg-Devonshire theory, we considered the impact of the flexoelectro-chemical coupling on the size effects inpolar properties and phase transitions of thin ferroelectric films with a layer of elastic defects. We investigated a typical case, when defects fill a thin layer below the top film surface with a constant concentration creating an additional gradient of elastic fields. The defective surface of the film is not covered with an electrode, but instead with an ultra-thin layer of ambient screening charges, characterized by a surface screening length. This geometry is typical for the scanning probe piezoelectric force microscopy. Obtained results revealed an unexpectedly strong effect of the joint action of Vegard stresses and flexoelectric effect (shortly flexo-chemical coupling) on the ferroelectric transition temperature, distribution of the spontaneous polarization and elastic fields, domain wall structure and period in thin PbTiO3 films containing a layer of elastic defects. A nontrivial result is the ferroelectricity persisting at film thicknesses below 4 nm, temperatures lower than 350 K and relatively high surface screening length (~0.1 nm). The origin of this phenomenon is the re-building of the domain structure in the film (namely the cross-over from c-domain stripes to a-type closure domains) when its thickness decreases below 4 nm, conditioned by the flexoelectric coupling and facilitated by negative Vegard effect. For positive Vegard effect, thicker films exhibit the appearance of pronounced maxima on the thickness dependence of the transition temperature, whose position and height can be controlled by the defect type and concentration. The revealed features may have important implications for miniaturization of ferroelectric-based devices.

cond-mat.mtrl-sci↗

arXiv2017

Flexocoupling induced soft acoustic mode and the spatially modulated phases in ferroelectrics

Using the Landau Ginzburg Devonshire theory and scalar approximation, we derived analytical expressions for the singular points (zeros, complex ranges) of the acoustic phonon mode (A mode) frequency in dependence on the wave vector k and examined the conditions of the soft A modes appearance in a ferroelectric depending on the magnitude of the flexoelectric coefficient f and temperature T. We predict that if the magnitude of the flexocoefficient f is equal to the temperature-dependent critical value fcr(T) at the temperature T=T_IC, the A mode frequency tends to zero at k=kr_0 and the spontaneous polarization becomes spatially modulated in a temperature range T<T_IC.The comparison of calculated physical properties with measured ones are performed for some ferroelectrics with SMP phases.In particular, temperature dependence of the calculated direct and inverse static dielectric susceptibility is in an agreement with experimental data in Sn2P2(SexS1-x)6 that gives us additional background to predict flexo-coupling induced soft acoustic amplitudon-type mode in the SMP phase.The available experimental data on neutron scattering in organic incommensurate ferroelectric (CH3)3NCH2COO*CaCl2*2H2O are in a semi-quantitative agreement with our theoretical results. To quantify the theory, it is necessary to measure the frequency dependence of the A mode in a uniaxial ferroelectric with a spatially modulated phase in the temperature interval near its occurrence.

cond-mat.mtrl-sci↗

arXiv2017

Size Effects of Ferroelectric and Magnetoelectric Properties of Semi-ellipsoidal Bismuth Ferrite Nanoparticles

Bismuth ferrite (BiFeO3) is one of the most promising multiferroics with a sufficiently high ferroelectric (FE) and antiferromagnetic transition temperatures, and magnetoelectric (ME) coupling coefficient at room temperature, and thus it is highly sensitive to the impact of cross-influence of applied electric and magnetic fields. According to the urgent demands of nanotechnology miniaturization for ultra-high density data storage in advanced nonvolatile memory cells, it is very important to reduce the sizes of multiferroic nanoparticles in the self-assembled arrays without serious deterioration of their properties. We study size effects of the phase diagrams, FE and ME properties of semi-ellipsoidal BiFeO3 nanoparticles clamped to a rigid conductive substrate. The spatial distribution of the spontaneous polarization vector inside the nanoparticles, phase diagrams and paramagnetoelectric (PME) coefficient were calculated in the framework of modified Landau-Ginzburg-Devonshire (LGD) approach. Analytical expressions were derived for the dependences of the FE transition temperature, average polarization, linear dielectric susceptibility and PME coefficient on the particle sizes for a general case of a semi-ellipsoidal nanoparticles with three different semi-axes a, b and height c. The analyses of the obtained results leads to the conclusion that the size effect of the phase diagrams, spontaneous polarization and PME coefficient is rather sensitive to the particle sizes aspect ratio in the polarization direction, and less sensitive to the absolute values of the sizes per se.

cond-mat.mtrl-sci↗

arXiv2016

Missed surface waves in non-piezoelectric solids

The physical processes taking place at the surface and near the surface of solids is so rich and versatile that sometimes they seem to be the inexhaustible subject of fundamental research. In particular, since the discovery by Lord Rayleigh surface waves in solids focus increased attention of scientists, because their experimental and theoretical studies can serve as the source of unique information about the surface impact on the dynamics and structure of the atomic lattice, structural instabilities and phase transitions induced by the surface, and explore the properties of phonons in spatially-confined systems The existence of purely shear surface wave is impossible in non-piezoelectrics within the framework of the classical theory of elasticity, because the Rayleigh surface waves have different polarization and are the mixture of shear and dilatational waves. We showed that the "forbidden" shear surface wave (shortly Flexo-SW) can propagate near the surface of all crystalline dielectrics due to the omnipresent flexoelectric coupling. The appearance and penetration depth of the Flexo-SW is ruled by the flexocoupling strength. In particular the penetration depth of transverse acoustic mode diverges in the absence of the flexoelectric coupling and so these waves become indistinguishable from the bulk waves. For paraelectrics such as strontium titanate with typical flexoeletric coefficients (~2V) the penetration depth of the Flexo-SW can reach more than tens microns at THz frequencies. The circumstances can explain the absence of experimental observations of the missed surface waves in thick layers and bulk materials. However we predict that the peaks of neutron intensity corresponding to the surface Flexo-SW and bulk phonon modes can be separated in non-piezoelectric thin films of thickness ~(20 - 50)nm.

cond-mat.mtrl-sci↗

arXiv2016

Flexocoupling impact on the size effects of piezo- response and conductance in mixed-type ferroelectrics-semiconductors under applied pressure

Flexocoupling impact on the size effects of the spontaneous polarization, effective piezo-response, elastic strain and compliance, carrier concentration and piezo-conductance have been calculated in thin films of ferroelectric semiconductors with mixed-type conductivity under applied pressure. Analysis of the self-consistent calculation results revealed that the thickness dependences of aforementioned physical quantities, calculated at zero and nonzero flexoelectric couplings, are very similar under zero applied pressure, but become strongly different under the application of external pressure pext. At that the differences become noticeably stronger for the film surface under compression than under tension. The impact of the Vegard mechanism on the size effects is weaker in comparison with flexocoupling except for the thickness dependence of the piezo-conductance. Without flexoelectric coupling the studied physical quantities manifest conventional peculiarities that are characteristic of the size-induced phase transitions. Namely, when the film thickness h approaches the critical thickness hcr the transition to paraelectric phase occurs. The combined effect of flexoelectric coupling and external pressure induces polarizations at the film surfaces, which cause the electric built-in field that destroys the thickness-induced phase transition to paraelectric phase at h= hcr and induces the electret-like state with irreversible spontaneous polarization at h<hcr. The built-in field leads to noticeable increase of the average strain and elastic compliance under the film thickness decrease below hcr that scales as 1/h at small thicknesses h. The changes of the electron concentration by several orders of magnitude under positive or negative pressures can lead to the occurrence of high- or low-conductivity states, i.e. the nonvolatile piezo-resistive switching.

cond-mat.mtrl-sci↗

arXiv2015

Reentrant phase in nanoferroics induced by the flexoelectric and Vegard effects

We explore the impact of the flexoelectric effect and Vegard effect (chemical pressure) on the phase diagrams, long-range polar order and related physical properties of the spherical ferroelectric nanoparticles using Landau-Ginzburg-Devonshire phenomenological approach. The synergy of these effects can lead to the remarkable changes of the nanoparticles' phase diagrams. In particular, a commonly expected transition from ferroelectric to paraelectric phase at some small critical size is absent; so that the critical size loses its sense. Contrary, the stabilization of the ferroelectric phase manifests itself by the enhancement of the transition temperature and polarization with the particle size decrease. Ferroelectric phase reentrant phenomenon was observed earlier in the tetragonal BaTiO3 nanospheres of radii 5-50 nm [Zhu et al., JAP 112, 064110 (2012)] and stayed unexplained up to now. Our calculations have shown the physical mechanism of the exciting phenomenon is the flexo-chemo-effect. Since the spontaneous flexoelectric coupling, as well as ion vacancies, should exist in any nanostructured ferroelectrics, obtained analytical results can be valid for many nanoferroelectrics, where reentrant phases appearance can be forecasted.

cond-mat.mtrl-sci↗

arXiv2015

Theoretical description of anomalous properties of novel room temperature multiferroics Pb(Fe1/2Ta1/2)x(Zr0.53Ti0.47)1-xO3 and Pb(Fe1/2Nb1/2)x(Zr0.53Ti0.47)1-xO3

The theoretical description of the anomalous ferroelectric, ferromagnetic and magnetoelectric properties of Pb(Fe1/2Ta1/2)x(Zr0.53Ti0.47)1-xO3 and Pb(Fe1/2Nb1/2)x(Zr0.53Ti0.47)1-xO3 micro-ceramics is given. We performed calculations of temperature, composition and external field dependence of ferroelectric, ferromagnetic and antiferromagnetic phases transition temperatures, remanent polarization, magnetization, hysteresis loops, coercive fields, dielectric permittivity and magnetoelectric coupling. Special attention was paid to comparison of the developed theory with experiments. It appeared possible to describe adequately the main experimental results including a reasonable agreement between the shape of calculated hysteresis loops and remnant polarization value with measured loops and polarization. Information about linear and nonlinear magnetoelectric coupling coefficients was extracted from the experimental data. From the fitting of experimental data with theoretical formula it appeared possible to obtain composition dependence of Curie-Weiss constant that is known to be inversely proportional to harmonic (linear) dielectric stiffness, as well as the strong nonlinear dependence of anharmonic parameters of free energy. Keeping in mind the essential influence of these parameters on the multiferroic properties the obtained results open the way to govern practically all the material properties with the help of suitable choice of composition. The forecast of the strong enough influence of antiferrodistortive order parameter on the transition temperatures and so on the phase diagrams and properties of multiferroics is made on the basis of the developed theory.

cond-mat.mtrl-sci↗

arXiv2015

Linear roto-antiferromagnetic effect in multiferroics: physical manifestations

Using the theory of symmetry and the microscopic model we predicted the possibility of a linear roto-antiferromagnetic effect in the perovskites with structural antiferrodistortive and antiferromagnetic long-range ordering and found the necessary conditions of its occurrence. The main physical manifestations of this effect are the smearing of the antiferromagnetic transition and the jump of the specific heat near it. In the absence of external fields linear roto-antiferromagnetic coupling can induce a weak antiferromagnetic ordering above the Neel temperature, but below the temperature of antiferrodistortive transition. Therefore, there is the possibility of observing weak antiferromagnetism in multiferroics such as bismuth ferrite (BiFeO3) at temperatures T>TN, for which the Neel temperature TN is about 645 K, and the antiferrodistortive transition temperature is about 1200 K. By quantitative comparison with experiment we made estimations of the linear roto-antiferromagnetic effect in the solid solutions of multiferroic Bi1-xRxFeO3 (R=La, Nd).

cond-mat.mtrl-sci↗