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 (k.lenczewska@intibs.pl).

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

50 days’ free access (up to 20.11.2018) LINK: https://authors.elsevier.com/a/1Xpxqc8qpEthw

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.

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)

DOI: https://doi.org/10.1007/978-3-319-99834-3 

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.

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.

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 (2018)

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.

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.

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 T∼ 690 K instead of T∼ 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.

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