This section collects all the official material created during the TransFerrr project as well as the publications that disseminate the results achieved by the project. If you are interested in communicating about TransFerr project get in contact with our dissemination manager Katarzyna Lenczewska (email@example.com).
Investigation of Local Conduction Mechanisms in Ca and Ti-Doped BiFeO3 Using Scanning Probe Microscopy Approach
Authors: Maxim S. Ivanov, Vladimir A. Khomchenko, Maxim V. Silibin, Dmitry V. Karpinsky, Carsten Blawert, Maria Serdechnova, José A. Paixão
DOI: https://doi.org/10.3390/nano10050940 Nanomaterials (2020) 10, 940
In this work we demonstrate the role of grain boundaries and domain walls in the local transport properties of n- and p-doped bismuth ferrites, including the influence of these singularities on the space charge imbalance of the energy band structure. This is mainly due to the charge accumulation at domain walls, which is recognized as the main mechanism responsible for the electrical conductivity in polar thin films and single crystals, while there is an obvious gap in the understanding of the precise mechanism of conductivity in ferroelectric ceramics. The conductivity of the Bi0.95Ca0.05Fe1−xTixO3−δ (x = 0, 0.05, 0.1; δ = (0.05 − x)/2) samples was studied using a scanning probe microscopy approach at the nanoscale level as a function of bias voltage and chemical composition. The obtained results reveal a distinct correlation between electrical properties and the type of charged defects when the anion-deficient (x = 0) compound exhibits a three order of magnitude increase in conductivity as compared with the charge-balanced (x = 0.05) and cation-deficient (x = 0.1) samples, which is well described within the band diagram representation. The data provide an approach to control the transport properties of multiferroic bismuth ferrites through aliovalent chemical substitution.
Postprint: OPEN ACCESS https://doi.org/10.3390/nano10050940
Magnetic Properties of La0.9A0.1MnO3 (A: Li, Na, K) Nanopowders and Nanoceramics
Authors: Paweł Głuchowski, Ruslan Nikonkov, Robert Tomala, Wiesław Strek, Tatsiana Shulha, Maria Serdechnova, Mikhail Zheludkevich, Andrius Pakalaniškis, Ramunas Skaudžius, Aivaras Kareiva, Alexander Abramov, Andrei Kholkin, Maxim V. Bushinsky, Dmitry Karpinsky
DOI: https://doi.org/10.3390/ma13071788 Materials (2020) 13, 1788
Nanocrystalline La0.9A0.1MnO3 (where A is Li, Na, K) powders were synthesized by a combustion method. The powders used to prepare nanoceramics were fabricated via a high-temperature sintering method. The structure and morphology of all compounds were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). It was found that the size of the crystallites depended on the type of alkali ions used. The high-pressure sintering method kept the nanosized character of the grains in the ceramics, which had a significant impact on their physical properties. Magnetization studies were performed for both powder and ceramic samples in order to check the impact of the alkali ion dopants as well as the sintering pressure on the magnetization of the compounds. It was found that, by using different dopants, it was possible to strongly change the magnetic characteristics of the manganites.
Postprint: OPEN ACCESS https://doi.org/10.3390/ma13071788
Nanoscale ferroelectricity in pseudo-cubic sol-gel derived barium titanate – bismuth ferrite (BaTiO3 – BiFeO3) solid solutions
Authors: A. Pakalniškis, A. Lukowiak, G. Niaura, P. Głuchowski, D. V. Karpinsky, D. O. Alikin, A. S. Abramov, A. Zhaludkevich, M. Silibin, A. L. Kholkin, R. Skaudžius, W. Strek, A. Kareiva
DOI: https://doi.org/10.1016/j.jallcom.2020.154632 Journal of Alloys and Compounds (2020) 830, 154632
Single phase barium titanate–bismuth ferrite ((1-x)BaTiO3-(x)BiFeO3, BTO-BFO) solid solutions were prepared using citric acid and ethylene glycol assisted sol-gel synthesis method. Depending on the dopant content the samples are characterized by tetragonal, tetragonal-pseudocubic, pseudocubic and rhombohedral structure as confirmed by Raman spectroscopy and XRD measurements. An increase of the BFO content leads to a reduction in the cell parameters accompanied by a decrease in polar distortion of the unit cell wherein an average particle size increases from 60 up to 350 nm. Non zero piezoresponse was observed in the compounds with pseudocubic structure while no polar distortion was detected in their crystal structure using X-ray diffraction method. The origin of the observed non-negligible piezoresponse was discussed assuming a coexistence of nanoscale polar and non-polar phases attributed to the solid solutions with high BFO content. A coexistence of the nanoscale regions having polar and non-polar character is considered as a key factor to increase macroscopic piezoresponse in the related compounds due to increased mobility of the domain walls and phase boundaries.
Nontrivial magnetic field related phenomena in the single-layer graphene on ferroelectric substrate
Authors: Maksym V. Strikha, Anna N. Morozovska, Zhanna G. Zemska
DOI: https://doi.org/10.1063/10.0000704 Fizika Nizkikh Temperatur (2020) 46, 261–270
The review is focused on our predictions of nontrivial physical phenomena taking place in the nanostructure single-layer graphene on ferroelectric substrate, which are related with magnetic field. In particular we predicted that 180-degree domain walls in a strained ferroelectric film can induce p-n junctions in a graphene channel and lead to the unusual temperature and gate voltage dependences of the perpendicular modes v┴ of the integer quantum Hall effect. The non-integer numbers and their irregular sequence principally differ from the conventional sequence v┴ = 3/2, 5/3, … The unusual v┴-numbers originate from significantly different numbers of the edge modes, v1 and v2, corresponding to different concentration of carriers in the left (n1) and right (n2) ferroelectric domains of p–n junction boundary. The difference between n1 and n2 disappears with the vanishing of the film spontaneous polarization in a paraelectric phase, which can be varied in a wide temperature range by an appropriate choice of misfit strain originated from the film-substrate lattice mismatch. Next we studied the electric conductivity of the system ferromagnetic dielectric-graphene channel-ferroelectric substrate. The magnetic dielectric locally transforms the band spectrum of graphene by inducing an energy gap in it and making it spin-asymmetric with respect to the free electrons. It was demonstrated, that if the Fermi level in the graphene channel belongs to energy intervals, where the graphene band spectrum, modified by EuO, becomes sharply spin-asymmetric, such a device can be an ideal non-volatile spin filter. The practical application of the system under consideration would be restricted by a Curie temperature of a ferromagnet. Controlling of the Fermi level (e.g., by temperature that changes ferroelectric polarization) can convert a spin filter to a spin valve.
Structural Properties of BiFeO3 and Bi0,9La0,1FeO3 Powders Synthesized by Sol-Gel Process
Authors: A. Semchenko, S. Khakhomov, V. Gaishun, D. Kovalenko, V. Sidsky, W. Strek, D. Hreniak
Engineering for Sustainable Future. INTER-ACADEMIA 2019, Vol. 101, pp. 113–118, Springer (2020)
The present work aims to design and study novel functional materials with multiferroic properties required in electric applications, such as magnetic and magnetoresistive sensors, actuators, microwave electronic devices, phase shifters, mechanical actuators etc. Complex oxides BiFeO3 and Bi0,9La0,1FeO3 for analysis of its structural properties were synthesized as powders by sol-gel method. The size, shape, and degree of crystallinity of the formed nanoparticles can be changed by varying the temperature and the concentrations of the initial reactants and the stabilizer. This work is devoted to interrelation between composition of sol-gel BiFeO3 and Bi0,9La0,1FeO3 nanopowders and their nanostructural properties.
Possible Electrochemical Origin of Ferroelectricity in HfO2 Thin Films
DOI: https://doi.org/10.1016/j.jallcom.2019.153628 Journal of Alloys and Compounds (2020) 830, 153628
Recent observations of unusual ferroelectricity in thin films of HfO2 and related materials has attracted broad interest to the materials and led to the emergence of a number of competing models for observed behaviors. Here we develop the analytical description for a possible electrochemical mechanism of observed ferroelectric-like behaviors, namely the collective phenomena of elastic and electric dipoles originated from oxygen vacancies. The vacancies are formed initially in the vicinity of film surfaces, grain boundaries, and other types of inhomogeneities inside the film including those induced by the film treatment. Electric cycling makes the distribution of electric dipoles more homogeneous than it was initially, providing at the same time the significant decrease in depolarization field. 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 α at P2 in the order-disorder type thermodynamic functional. Negative coefficient α 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 (5–20) μC/cm2, can be induced by oxygen vacancies in HfO2 films of thickness less than (20–30) nm. Semi-quantitative agreement with available experimental data is demonstrated.
Preprint deposited in the repository: https://arxiv.org/abs/1811.09787
Analytical description of the size effect on pyroelectric and electrocaloric properties of ferroelectric nanoparticles
Authors: Anna N. Morozovska, Eugene A. Eliseev, Maya D. Glinchuk, Hanna V. Shevliakova, George S. Svechnikov, Maxim V. Silibin, Artem V. Sysa, Andrii D. Yaremkevich, Nicholas V. Morozovsky, Vladimir V. Shvartsman
DOI: https://doi.org/10.1103/PhysRevMaterials.3.104414 J. Phys. Rev. Materials (2019) 3, 104414
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 of spherical single-domain ferroelectric nanoparticles. The considered physical model corresponds to the nanocomposite with a small fraction of ferroelectric nanoparticles. Within the framework of the analytical model, we establish how the size changes determine the temperature and field behavior of pyroelectric and electrocaloric coefficients on the 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 and height. Obtained analytical expressions allow selecting the interval of particle sizes, voltage, and/or temperature for which the 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.
Preprint deposited in the repository: https://arxiv.org/abs/1906.02953
Mapping gradient-driven morphological phase transition at the conductive domain walls of strained multiferroic films
DOI: https://link.aps.org/doi/10.1103/PhysRevB.100.104109 Physical Review B (2019) 100, 104109
The coupling between antiferrodistortion (AFD) and ferroelectric (FE) polarization, universal for all tilted perovskite multiferroics, is known to strongly correlate with domain wall functionalities in the materials. The intrinsic mechanisms of domain wall phenomena, especially AFD-FE coupling-induced phenomena at the domain walls, have continued to intrigue the scientific and technological communities because of the need to develop future nanoscale electronic devices. Over the past years, theoretical studies have often shown controversial results, owing to the fact that they are neither sufficiently nor directly corroborated with experimental evidence. In this work, the AFD-FE coupling at uncharged 180° and 71° domain walls in BiFeO3 films is investigated by means of aberration-corrected scanning transmission electron microscopy with high-resolution scanning transmission electron microscopy and rationalized by phenomenological Landau-Ginzburg-Devonshire (LGD) theory. We reveal a peculiar morphology at the AFD-FE walls, including kinks, meandering, and trianglelike regions with opposite oxygen displacements and curvature near the interface. The LGD theory confirms that the tilt gradient energy induces these unusual morphologies and the features would change delicately with different kinds of domain walls. Moreover, the 180° AFD-FE walls are proved to be conductive with an unexpected reduction of the Fe-O-Fe bond angle, which is distinct from theoretical predictions. By exploring AFD-FE coupling at the domain walls, and its induced functionalities, we provide exciting evidence into the links between structural distortions and its electronic properties, which provide great benefit for fundamental understanding of domain wall functionalities as well as functional manipulations for novel nanodevices.
Preprint deposited in the repository: https://arxiv.org/abs/1903.05531
Novel synthetic approach to the preparation of single-phase BixLa1−xMnO3+δ solid solutions
DOI: https://doi.org/10.1007/s10971-019-05098-w Journal of Sol-Gel Science and Technology (2019) 93, 650–656
In this study, the BixLa1−xMnO3+δ solid solutions (x from 0 to 0.65) were synthesized using sol–gel combustion method with citric acid as a fuel and complexing agent. It was shown that changes in chemical composition of the materials lead to the evolution of crystal structure, morphology, and magnetic properties. The thermal behavior of precursor gel was investigated by thermogravimetric and differential scanning calorimetry (TG-DSC) measurements. X-ray diffraction (XRD) analysis demonstrated that all samples were monophasic. The Rietveld analysis showed that the structure can be indexed by trigonal or cubic unit cell depending on Bi3+ content. Scanning electron microscopy (SEM) was used to evaluate morphological features of the synthesized materials and revealed that Bi3+ ions significantly promote growth of the grains. The sol–gel-derived BixLa1−xMnO3+δ specimens were also characterized by FT-IR spectroscopy and magnetization measurements, which showed a clear correlation between magnetic properties and crystal structure of the materials.
Ferromagnetic-like behavior of Bi0.9La0.1FeO3–KBr nanocomposites
Authors: D.V. Karpinsky, O.M. Fesenko, M.V. Silibin, S.V. Dubkov, M. Chaika, A. Yaremkevich, A. Lukowiak, Y. Gerasymchuk, W. Stręk, A. Pakalniškis, R. Skaudzius, A. Kareiva, Y.M. Fomichov, V.V. Shvartsman, S.V. Kalinin, N.V. Morozovsky, A.N. Morozovska
DOI: https://doi.org/10.1038/s41598-019-46834-0 Scientific Reports (2019) 9, 10417
We studied magnetostatic response of the Bi0.9La0.1FeO3– KBr composites (BLFO-KBr) consisting of nanosized (≈100 nm) ferrite Bi0.9La0.1FeO3 (BLFO) conjugated with fine grinded ionic conducting KBr. When the fraction of KBr is rather small (less than 15 wt%) the magnetic response of the composite is very weak and similar to that observed for the BLFO (pure KBr matrix without Bi1-xLaxFeO3 has no magnetic response as anticipated). However, when the fraction of KBr increases above 15%, the magnetic response of the composite changes substantially and the field dependence of magnetization reveals ferromagnetic-like hysteresis loop with a remanent magnetization about 0.14 emu/g and coercive field about 1.8 Tesla (at room temperature). Nothing similar to the ferromagnetic-like hysteresis loop can be observed in Bi1-zLazFeO3 ceramics with z ≤ 0.15, which magnetization quasi-linearly increases with magnetic field. Different physical mechanisms were considered to explain the unusual experimental results for BLFO-KBr nanocomposites, but only those among them, which are highly sensitive to the interaction of antiferromagnetic Bi0.9La0.1FeO3 with ionic conductor KBr, can be relevant.
Preprint deposited in the repository: https://arxiv.org/abs/1901.08913
Indentation induced local polarization reversal in La doped BiFeO3 ceramics
DOI: https://doi.org/10.1080/00150193.2019.1574634 Ferroelectrics (2019) 541, 1-9
Stress-induced local polarization reversal was studied in La doped BiFeO3 ceramics under the action of Berkovich-type prism indentation. Piezoresponse force microscopy was used for detailed study of domain structure before and after local polarization reversal. Two mechanisms of domain formation under the action of the mechanical loading were revealed: (1) direct stress-induced and (2) stress mediated by grain clamping. Critical stress value for local polarization reversal was extracted from the dependence of the switched area on the applied loading force.
Building Free Energy Functional from Atomically-Resolved Imaging: Atomic Scale Phenomena in La-doped BiFeO3
DOI: https://link.aps.org/doi/10.1103/PhysRevB.99.195440 Physical Review B (2019) 99, 195440
Scanning transmission electron microscopy (STEM) has enabled mapping of atomic structures of solids with sub-picometer precision, providing insight to the physics of ferroic phenomena and chemical expansion. However, only a subset of information is available, due to projective nature of imaging in the beam direction. Correspondingly, the analysis often relies on the postulated form of macroscopic Landau-Ginzburg energy for the ferroic long-range order parameter, and some predefined relationship between experimentally determined atomic coordinates and the order-parameter field. Here, we propose an approach for exploring the structure of ferroics using reduced order-parameter models constructed based on experimental data only. We develop a four-sublattice model (FSM) for the analytical description of A-cation displacement in (anti)ferroelectric-antiferrodistortive perovskites of ABO3 type. The model describes the displacements of cation A in four neighboring unit cells and determines the conditions of different structural phases’ appearance and stability in ABO3. We show that FSM explains the coexistence of rhombohedral, orthorhombic, and spatially modulated phases, observed by atomic-resolution STEM in La-doped BiFeO3. Using this approach, we atomically resolve and theoretically model the sublattice asymmetry inherent to the case of the A-site La/Bi cation sublattice in LaxBi1−xFeO3 polymorphs. This approach allows the exploration of ferroic behaviors from experimental data only, without additional assumptions on the nature of the order parameter.
Postprint deposited in the repository: https://arxiv.org/abs/1903.03656
A-site ordered state in manganites with perovskite-like structure based on the optimally doped compounds Ln0.70Ba0.30MnO3 (Ln = Pr, Nd)
DOI: https://doi.org/10.1016/j.jre.2018.12.010 Journal of Rare Earths (2019) 37, 1242-1249
In this paper, we report on the crystal structure and magnetic properties of the nanostructured Ba-ordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln0.70Ba0.30MnO3 (Ln = Pr, Nd). The materials were studied by X- ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and SQUID- magnetometry techniques. It is found that states with different degrees of cation ordering in the A– sublattice of the ABO3 perovskite can be obtained by employing special conditions of chemical treatment. In particular, reduction of the parent compounds results in the formation of a nanocomposite containing ferrimagnetic anion-deficient ordered phase LnBaMn2O5. Oxidation of the composite does not change an average size of the nanocrystallites, but drastically alters their phase composition to stabilize ferromagnetic stoichiometric ordered phase LnBaMn2O6 and ferromagnetic superstoichiometric disordered phase Ln0.90Ba0.10MnO3+δ. It is shown that the magnetic properties of the materials are determined by the joint action of chemical (cation ordering) and external (surface tension) pressures.
Size effect of soft phonon dispersion in nanosized ferroics
DOI: https://doi.org/10.1103/PhysRevB.99.115412 Physical Review B (2019) 99, 115412
Using Landau-Ginsburg-Devonshire theory, we derive and analyze analytical expressions for the frequency dispersion of soft phonon modes in nanosized ferroics and perform numerical calculations for a thin SrTiO3 film. We revealed the pronounced “true” size effect in the dependence of soft phonon spatial dispersion on the film thickness and predict that it can lead to the “apparent” or “false” size effect of dynamic flexoelectric coupling constants. Also, we derived analytical expressions describing the influence of finite size effect on the appearance and properties of the incommensurate spatial modulation induced by the static flexoelectric effect in ferroic thin films. To verify the theoretical predictions experimental measurements of the soft phonon dispersion in nanosized ferroics seem urgent.
Preprint deposited in the repository: http://arxiv.org/abs/1812.04702
Intrinsic structural instabilities of domain walls driven by gradient coupling: Meandering antiferrodistortive-ferroelectric domain walls in BiFeO3
DOI: https://doi.org/10.1103/PhysRevB.99.014112 Physical Review B (2019) 99, 014112
Using the Landau-Ginzburg-Devonshire approach, we predict the intrinsic instability of the ferroelectric-ferroelastic domain walls in the multiferroic BiFeO3 emerging from the interplay between the gradient terms of the antiferrodistortive and ferroelectric order parameters at the walls. These instabilities are the interface analog of the structural instabilities in the vicinity of phase coexistence in the bulk, and so they do not stem from incomplete polarization screening in thin films or its spatial confinement, electrostrictive or flexoelectric coupling. The effect of BiFeO3 material parameters on the 71∘, 109∘, and 180∘ walls is explored, and it is shown that the meandering instability appears at 109∘ and 180∘walls for small gradient energies, and the walls become straight and broaden for higher gradients. In contrast to the 180∘ and 109∘ domain walls, uncharged 71∘ walls are always straight, and their width increases with increasing the tilt gradient coefficient. The wall instability and associated intrinsic meandering provide insight into the behavior of morphotropic and relaxor materials, wall pinning, and mechanisms of interactions between order parameter fields and local microstructure.
Preprint deposited in the repository: https://arxiv.org/abs/1810.06668
Optical, Dielectric and Magnetic Properties of La1−xNdxFeO3 Powders and Ceramics
DOI: https://doi.org/10.3390/ceramics2010001 Ceramics (2019) 2, 1-12
Nanocrystalline La1−xNdxFeO3 powders with different concentrations of Nd3+ have been synthesized using a modified Pechini method. Their structures were studied by X-ray powder diffraction (XRD). Furthermore, La1−xNdxFeO3 nanoceramics were prepared using a high pressure sintering technique. The luminescence spectra of the powders were investigated as a function of concentration of active dopant to check the possible energy transfers observed due to Nd3+ concentration changes. The electrical and magnetic properties of the powders and ceramics were investigated to determine the effect of Nd3+ doping on the dielectric permittivity and magnetization in the wide frequency range.
Preprint deposited in the repository: https://www.preprints.org/manuscript/201811.0411/v1
Integer quantum Hall effect in graphene channel with p-n junction at domain wall in a strained ferroelectric film
DOI: https://doi.org/10.1063/1.5052546 Journal of Applied Physics (2019) 125, 082525
We revealed that 180° domain walls in a strained ferroelectric film can induce p-n junctions in a graphene channel and lead to the nontrivial temperature and gate voltage dependences of the perpendicular modes of the integer quantum Hall effect (IQHE). In particular, the number of perpendicular modes v⊥, corresponding to the p-n junction across the graphene channel, varies with the gate voltage increase from small integers to higher non-integer numbers, e.g., v⊥ = 1.9, 2, …, 5.1, 6.875, …, 9.1, …, 23,…, 37.4, in the vicinity of the transition temperature from the ferroelectric to paraelectric phase. The non-integer numbers and their irregular sequence principally differ from the sequence of non-integer numbers ν = 3/2, 5/3, … reported earlier. The unusual v⊥-numbers originate from significantly different numbers of the edge modes, ν1 and ν2, corresponding to different concentrations of carriers in the left (n1) and right (n2) domains of the p-n junction boundary. The concentrations n1 and n2 are determined by the gate voltage and spontaneous polarization contributions, and so their difference originates from different directions of the spontaneous polarization in different domains of the strained ferroelectric film. The difference between n1 and n2disappears with the vanishing of the film spontaneous polarization in a paraelectric phase. The temperature transition from the ferroelectric to paraelectric phase taking place in a strained ferroelectric film can be varied in a wide temperature range by an appropriate choice of misfit strain so that the first plateaus of the predicted IQHE effect can be observed even at room temperatures.
Preprint deposited in the repository: https://arxiv.org/abs/1802.07764
Anomalies of phase diagrams and physical properties of antiferrodistortive perovskite oxides
DOI: https://doi.org/10.1016/j.jallcom.2018.11.015 Journal of Alloys and Compounds (2019) 778, 452-479
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 perovskites, 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 theory 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 octahedra 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.
Noteworthy, the results obtained within LGD approach show the possibility of controlling multiferroicity, including FE, FM and AFM phases in bulk and nanosized AFD ferroics, with the help of size effects and/or electric/magnetic field application. Since theoretical results are in qualitative agreement with experimental results, we conclude that LGD theory can be successfully applied to many AFD perovskite oxides.
Postprint deposited in the repository: https://arxiv.org/abs/1807.01743
Analytical description of domain morphology and phase diagrams of ferroelectric nanoparticles
Authors: Anna N. Morozovska, Yevhen M. Fomichоv, Petro Maksymovych, Yulian M. Vysochanskii, and Eugene A. Eliseev
DOI: https://doi.org/10.1016/j.actamat.2018.08.051 Acta Materialia (2018) 160, 109-120
Analytical description of domain structure morphology and phase diagrams of ferroelectric nanoparticles is developed in the framework of Landau-Ginzburg-Devonshire approach. To model realistic conditions of incomplete screening of spontaneous polarization at the particle surface, it was considered covered by an ultra-thin layer of screening charge with effective screening length. The phase diagrams, calculated for spherical Sn2P2S6 nanoparticles in coordinates “temperature” and “effective screening length” by finite element modelling, demonstrate the emergence of poly-domain region at the tricritical point and its broadening with increasing the screening length for the particle radius over a critical value. Metastable and stable labyrinthine domain structures exist in Sn2P2S6 nanoparticles with radius (8–10) nm and more. We derived simple analytical expressions for the boundaries between paraelectric, single-domain and poly-domain ferroelectric phases, tricritical point and the necessary condition for the appearance of labyrinthine domains, and demonstrated their high accuracy in comparison with finite element modelling results.
Analytical expressions for the dependence of the ferroelectric-paraelectric transition temperature on the particle radius in the single-domain and poly-domain states of the particle were compared with analogous dependences experimentally measured for SrBi2Ta2O9 nanoparticles and simulated for Sn2P2S6 nanocrystals by Monte Carlo method within the framework of axial next-nearest-neighbours Ising model. The analytical expression for the ferroelectric-paraelectric transition temperature in the poly-domain state quantitatively agrees with experimental and simulated results, and it accurately reproduces empirical Ishikawa equation at all temperatures, justifying it theoretically. Analytical description shows that phase diagrams and domain morphologies, which are qualitatively similar to the ones calculated in this work, can be expected in other ferroelectric nanoparticles covered by the screening charges, being rather different for the ferroelectrics with the first and second order ferroelectric-paraelectric transitions respectively.
Preprint deposited in the repository: https://arxiv.org/abs/1805.11134
Temperature behavior of graphene conductance induced by piezoelectric effect in a ferroelectric substrate
Authors: A. Morozovska, A. Kurchak, Z. Zemska, A. Lukowiak, M. Strikha
DOI: https://doi.org/10.1063/1.5034340 Journal of Applied Physics (2018) 124, 084103
Graphene on a ferroelectric can be a promising candidate to create advanced field effect transistors, modulators and electrical transducers. Recently we have shown that alternating “up” and “down” piezoelectric displacement of the ferroelectric domain surfaces can lead to the increase of graphene channel conductance at room temperature because of partial separation of the graphene channel from the ferroelectric substrate. The change of graphene conductance caused by piezoelectric effect requires systematic studies of ambient conditions impact on its manifestations. Present theoretical work studies the temperature behavior of the graphene conductance changes induced by piezoelectric effect in a ferroelectric substrate with domain structure. We revealed the possibility of increasing up to 100 times the conductance of the graphene channel on ferroelectric substrate by changing the ambient temperature for a given gate voltage and channel length. Obtained results can open the way towards advanced applications of graphene on ferroelectric in piezo-resistive memories operating in a wide temperature range.
Postprint deposited in the repository: https://arxiv.org/abs/1804.03175
Synthesis of BiFeO3-Powders by Sol-Gel Process
Authors: S.A. Khakhomov, V.E. Gaishun, D.L. Kovalenko, A.V. Semchenko, V.V. Sidsky, W. Strek, D. Hreniak, A. Lukowiak, N.S. Kovalchuk, A.N. Pyatlitski, V.A. Solodukha, D. V. Karpinsky
Recent Advances in Technology Research and Education. INTER-ACADEMIA 2018, Vol. 53, pp. 43 – 48, Springer (2019)
The present work aims to design and study novel functional materials with multiferroic properties required in electric applications, such as magnetic and magnetoresistive sensors, actuators, microwave electronic devices, phase shifters, mechanical actuators etc. Complex oxides BiFeO3 for analysis of its magnetic properties were synthesized by sol-gel method as powders. The size, shape and degree of crystallinity of the nanoparticles formed by sol-gel method can be controlled by varying the temperature and the ratio of the concentrations of the initial reactants and the stabilizer. To stop the growth of particles in all cases, it is usually enough to cool quickly the reaction mixture. To isolate the nanoparticles, the precipitating solvent is added, which mixes with the reaction system, but poorly dissolves the “protective shells” of the nanoparticles and, therefore, destabilizes the suspension. As a result, the nanoparticles precipitate as powder, which can be separated by centrifugation. The sol-gel method makes it possible to obtain practically monodisperse nanoparticles of various metals oxides.
Structure and piezoelectric properties of Sm-doped BiFeO3 ceramics near the morphotropic phase boundary
Authors: D.V.Karpinsky, I.O.Troyanchuk A.V.Trukhanov, M.Willinger, V.A.Khomchenko, A.L.Kholkin, V.Sikolenko, T.Maniecki, W.Maniukiewicz, S.V.Dubkov, M.V.Silibin
DOI: https://doi.org/10.1016/j.materresbull.2018.08.002 Materials Research Bulletin (2019) 112, 420-425
The evolution of crystal structure and piezoelectric properties of the Bi1-xSmxFeO3 ceramics with compositions corresponding to the phase boundary region between the polar rhombohedral and anti-polar orthorhombic phases have been studied. The materials have been investigated using X-ray diffraction, transmission electron microscopy and piezoresponse force microscopy techniques. The diffraction measurements have allowed studying the crystal structure transformations depending on the dopant concentration and temperature. Similar to the compounds with x > 0.18, the lightly-doped samples have been found to adopt the non-polar orthorhombic structure at elevated temperatures. The research has clarified the correlation between the structural state and piezoelectric behavior. Substantial increase in piezoresponse observed for the phase-separated compounds having a dominant fraction of the rhombohedral phase has been discussed assuming significant extrinsic contribution associated with a metastable structural state changing under external electric field.
Fixed Volume Effect on Polar Properties and Phase Diagrams of Ferroelectric Semi-ellipsoidal Nanoparticles
Authors: Eugene A. Eliseev, Victoria V. Khist, Yevhen M. Fomichov, Maxim V. Silibin, George S. Svechnikov, Andrei L. Kholkin, Dmitry V. Karpinsky, Vladimir V. Shvartsman and Anna N. Morozovska
DOI: https://doi.org/10.1140/epjb/e2018-90133-6 The European Physical Journal B () 91, 150
For advanced applications in modern industry, it is very important to reduce the volume of ferroelectric nanoparticles without serious deterioration of their polar properties. In many practically important cases, the fixed volume (rather than the fixed size) corresponds to realistic technological conditions of nanoparticles fabrication. The letter is focused on the theoretical study of the behavior of ferroelectric polarization, paramagnetoelectric coefficient and phase diagrams of semi-ellipsoidal nanoparticles with a fixed volume V. Our approach combines the Landau-Ginzburg-Devonshire phenomenology, the classical electrostatics, and the elasticity theory. Our results show that the size effects on the phase diagrams and polarization of semi-ellipsoidal BiFeO3 nanoparticles nontrivially depend on V. These findings provide a path to optimize the polar properties of nanoparticles by controlling their phase diagrams at a fixed volume.
Preprint deposited in the repository: https://arxiv.org/abs/1707.06646
Rotomagnetic coupling in fine-grained multiferroic BiFeO3: Theory and experiment
Authors: Anna N. Morozovska, Eugene A. Eliseev, Maya D. Glinchuk, Olena M. Fesenko, Vladimir V. Shvartsman, Venkatraman Gopalan, Maxim V. Silibin, and Dmitry V. Karpinsky
DOI: https://doi.org/10.1103/PhysRevB.97.134115 Physical Review B () 97, 134115
Using Landau-Ginzburg-Devonshire (LGD) theory for BiFeO3 dense fine-grained ceramics with quasispherical grains and nanosized intergrain spaces enriched by elastic defects, we calculated a surprisingly strong size-induced increase in the antiferromagnetic transition temperature caused by the joint action of rotomagnetic and magnetostrictive coupling. Notably, all parameters included in the LGD functional have been extracted from experiments, not assumed. Complementarily, we performed experiments for dense BiFeO3 ceramics, which revealed that the shift of the antiferromagnetic transition is to TN ∼ 690 K instead of TN ∼ 645 K for a single crystal. To explain the result theoretically, we consider the possibility of controlling the antiferromagnetic state of multiferroic BiFeO3 via biquadratic antiferrodistortive rotomagnetic, rotoelectric, magnetoelectric, and magnetostrictive couplings. According to our calculations, the highest contribution is the rotostriction contribution, while the magnetostrictive and electrostriction contributions appear smaller.
Preprint deposited in the repository: https://arxiv.org/abs/1803.02805
Nontrivial temperature behavior of the carrier concentration in graphene on ferroelectric substrate with domain walls
Authors: Anatolii I. Kurchak, Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Maksym V. Strikha
DOI: https://doi.org/10.1016/j.actamat.2018.04.036 Acta Materialia (2018) 155, 302-317
This work explores a nontrivial temperature behavior of the carriers concentration, which governs the conductance of the graphene channel on ferroelectric substrate with domain walls that is a basic element for field effect transistors of new generation. We revealed the transition from a single to double antiferroelectric-like hysteresis loop of the concentration voltage dependence that happens with the temperature increase and then exist in a wide temperature range (350–500) K. We have shown that the double loops of polarization and concentration can have irregular shape that remains irregular as long as the computation takes place, and the voltage position of the different features (jumps, secondary maxima, etc) changes from one period to another, leading to the impression of quasi-chaotic behavior. It appeared that these effects originate from the nonlinear screening of ferroelectric polarization by graphene carriers, as well as it is conditioned by the temperature evolution of the domain structure kinetics in ferroelectric substrate. The nonlinearity rules the voltage behavior of polarization screening by graphene 2D-layer and at the same time induces the motion of separated domain walls accompanied by the motion of p-n junction along the graphene channel. Since the domain walls structure, period and kinetics can be controlled by changing the temperature, we concluded that the considered nano-structures based on graphene-on-ferroelectric are promising for the fabrication of new generation of modulators based on the graphene p-n junctions.
Postprint deposited in the repository: https://arxiv.org/abs/1712.03271
Polar-antipolar transition and weak ferromagnetism in Mn-doped Bi0.86La0.14FeO3
Authors: V. A. Khomchenko, D. V. Karpinsky, I. O. Troyanchuk, V. V. Sikolenko, D. M. Többens, M. S. Ivanov, M. V. Silibin, R. Rai, J. A. Paixão
DOI: https://doi.org/10.1088/1361-6463/aab58f J. Phys. D: Appl. Phys. (2018) 51, 165001
Having been considered as a prime example of a room-temperature magnetoelectric multiferroic, BiFeO3 continues to attract much interest. Since functional properties of this material can be effectively influenced by chemical, electrical, magnetic, mechanical and thermal stimuli, it can serve as a model for the investigation of cross-coupling phenomena in solids. Special attention is currently paid to the study of chemical pressure-driven magneto-structural transformations. In this paper, we report on the effect of the Mn doping on the crystal structure and magnetic behavior of the Bi1−x La xFeO3 multiferroics near their polar-antipolar (antiferromagnetic-weak ferromagnetic) phase boundary. Synchrotron x-ray and neutron powder diffraction measurements of the Bi0.86La0.14Fe1−xMn x O3 (x = 0.05, 0.1, 0.15) compounds have been performed. The diffraction data suggest that the Mn substitution results in the suppression of the ferroelectric polarization and gives rise to the appearance of the antiferroelectric (generally, PbZrO3-related) phase characteristic of the phase diagrams of the Bi1−x RE x FeO3 (RE = rare-earth) systems. Depending on the Mn concentration (determining phase composition of the Bi0.86La0.14Fe1−x Mn x O3 samples at room temperature), either complete or partial revival of the polar phase can be observed with increasing temperature. Magnetic measurements of the samples indicate that the Mn doping affects the stability of the cycloidal antiferromagnetic order specific to the polar phase, thus resulting in the formation of a ferroelectric and weak ferromagnetic state.
Preprint deposited in the repository: http://hdl.handle.net/10316/81273
Local electromechanical characterization of Pr doped BiFeO3 ceramics
Authors: A. S. Abramov, D. O. Alikin, M. M. Neradovskiy, A. P. Turygin, A. D. Ushakov, R. O. Rokeah, A. V. Nikitin, D. V. Karpinsky, V. Ya. Shur, A. L. Kholkin
DOI: https://doi.org/10.1080/00150193.2018.1432930 Ferroelectrics (2018) 525, 64-75
Local electromechanical (EM) measurements were performed in Pr doped BiFeO3(BPFO) ceramics via piezoresponse force microscopy (PFM). The results revealed that local EM response was different from the macroscopic one due to the large contribution of the leakage current. The locally measured response was used to evaluate effective piezoelectric coefficient d33 of the material. The multi-frequency PFM mode with additional compensation of the cantilever-surface Coulomb interaction under application of the external DC bias provided the most accurate values of the effective d33 coefficient and allowed studying its surface distribution and residual depolarization field distribution across the surface of BPFO ceramics.
Magnetic and dipole moments in indium doped barium hexaferrites
Authors: S.V.Trukhanov, A.V.Trukhanov, V.A.Turchenko, An.V.Trukhanov, D.I.Tishkevich, E.L.Trukhanova, T.I.Zubar, D.V.Karpinsky, V.G.Kostishyn, L.V.Panina, D.A.Vinnik, S.A.Gudkova, E.A.Trofimov, P.Thakur, A.Thakur, Y.Yang
DOI: https://doi.org/10.1016/j.jmmm.2018.02.078 Journal of Magnetism and Magnetic Materials () 457, 83-96
Crystal and magnetic structure of the doped BaFe12−xInxO19 samples were refined by the results of investigations using high resolution neutron powder diffraction and vibration sample magnetometry at different temperatures. The refinements were realized in frame of two space groups. The P63/mmc (No 194) centrosymmetric nonpolar and P63mc (No 186) noncentrosymmetric polar space groups were used. The unit cell parameters, ionic coordinates, thermal isotropic factors, occupation positions, bond lengths and bond angles, microstrain values were established. The magnetic and dipole moments were also defined. It is established that the In3+ cations may be located only in the Fe1 – 2a and Fe2 – 2b crystallographic positions with equal probability for the sample with lowest substitution level x = 0.1. At the x = 1.2 substitution level about half of the In3+ cations occupies the Fe5 – 12 k positions. For the last sample the remaining half of the In3+ cations is equiprobably located in the Fe1 – 2a and Fe2 – 2b positions. The spontaneous polarization was established for these compositions at 300 K. It is studied the influence of the type of substitutive cation and structural parameters on the Fe3+(i) – O2− – Fe3+(j) (i, j = 1, 2, 3, 4, 5) indirect superexchange interactions with temperature. With substitution level increase the superexchange interactions between the magnetic positions inside and outside the sublattices are broken which leads to a decrease in the value of their magnetic moments.
Flexoelectricity induced spatially modulated phases in ferroics and liquid crystals
Authors: Anna N. Morozovska, Victoria V. Khist, Maya D. Glinchuk, Christian M. Scherbakov, Maxim V. Silibin, Dmitry V. Karpinsky, Eugene A. Eliseev
DOI: https://doi.org/10.1016/j.molliq.2018.01.052 Journal of Molecular Liquids () 267, 550-559
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 liquid crystals displays.
Preprint deposited in the repository: https://arxiv.org/abs/1710.01033