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 (firstname.lastname@example.org).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.