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Morozovska, A. N.

Publications and source records attributed to Morozovska, A. N..

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Intrinsic structural instabilities of domain walls driven by gradient coupling: Meandering antiferrodistortive-ferroelectric domain walls in BiFeO 3

Using the Landau-Ginzburg-Devonshire approach, we predict the intrinsic instability of the ferroelectric-ferroelastic domain walls in the multiferroic BiFeO 3 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 BiFeO 3 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. As a result, 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.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrafast current imaging by Bayesian inversion

Spectroscopic measurements of current–voltage curves in scanning probe microscopy is the earliest and one of the most common methods for characterizing local energy-dependent electronic properties, providing insight into superconductive, semiconductor, and memristive behaviors. However, the quasistatic nature of these measurements renders them extremely slow. Here, we demonstrate a fundamentally new approach for dynamic spectroscopic current imaging via full information capture and Bayesian inference. This general-mode I–V method allows three orders of magnitude faster measurement rates than presently possible. The technique is demonstrated by acquiring I–V curves in ferroelectric nanocapacitors, yielding >100,000 I–V curves in <20 min. This allows detection of switching currents in the nanoscale capacitors, as well as determination of the dielectric constant. These experiments show the potential for the use of full information capture and Bayesian inference toward extracting physics from rapid I–V measurements, and can be used for transport measurements in both atomic force and scanning tunneling microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Tuning the polar states of ferroelectric films via surface charges and flexoelectricity

In this work, using the self-consistent Landau-Ginzburg-Devonshire approach we simulate and analyze the spontaneous formation of the domain structure in thin ferroelectric films covered with the surface screening charge represented by the Bardeen-type surface states. Hence we consider the competition between the screening and the domain formation as alternative ways to reduce the electrostatic energy and reveal unusual peculiarities of distributions of polarization, electric and elastic fields conditioned by the surface screening length and the flexocoupling strength. We have established that the critical thickness of the film and its transition temperature to a paraelectric phase strongly depend on the Bardeen screening length, while the flexocoupling affects the polarization rotation and closure domain structure. Furthermore the flexocoupling induces ribbon-like nano-scale domains in the film depth far from the top open surface, which might be related to the enigmatic polar nanoregions in relaxor ferroelectrics. Thus the joint action of the surface screening (originating from e.g. the adsorption of ambient ions or surface states) and flexocoupling may remarkably modify polar and electromechanical properties of thin ferroelectric films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Self-consistent modelling of electrochemical strain microscopy in mixed ionic-electronic conductors: Nonlinear and dynamic regimes

The frequency dependent Electrochemical Strain Microscopy (ESM) response of mixed ionic-electronic conductors is analyzed within the framework of Fermi-Dirac statistics and the Vegard law, accounting for steric effects from mobile donors. The emergence of dynamic charge waves and nonlinear deformation of the surface in response to bias applied to the tip-surface junction is numerically explored. The 2D maps of the strain and concentration distributions across the mixed ionic-electronic conductor and bias-induced surface displacements are calculated. The obtained numerical results can be applied to quantify the ESM response of Li-based solid electrolytes, materials with resistive switching, and electroactive ferroelectric polymers, which are of potential interest for flexible and high-density non-volatile memory devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Electroelastic fields in artificially created vortex cores in epitaxial BiFeO 3 thin films

Here we employ phase-field modeling to explore the elastic properties of artificially created 1-D domain walls in (001) p -oriented BiFeO 3 thin films, composed of a junction of the four polarization variants, all with the same out-of-plane polarization. It was found that these junctions exhibit peculiarly high electroelastic fields induced by the neighboring ferroelastic/ferroelectric domains. The vortex core exhibits a volume expansion, while the anti-vortex core is more compressive. We also discuss possible ways to control the electroelastic field, such as varying material constant and applying transverse electric field.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Ferroelectric Switching by the Grounded Scanning Probe Microscopy Tip

The process of polarization reversal by the tip of scanning probe microscope was intensively studied for last two decades. Number of the abnormal switching phenomena was reported by the scientific groups worldwide. In particularly it was experimentally and theoretically shown that slow dynamics of the surface screening controls kinetics of the ferroelectric switching, backswitching and relaxation and presence of the charges carriers on the sample surface and in the sample bulk significantly change polarization reversal dynamics. Here we experimentally demonstrated practical possibility of the history dependent polarization reversal by the grounded SPM tip. This phenomenon was attributed to induction of the slowly dissipating charges into the surface of the grounded tip that enables polarization reversal under the action of the produced electric field. Analytical and numerical electrostatic calculations allow additional insight into nontrivial abnormal switching phenomena reported earlier.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Observation of a periodic array of flux-closure quadrants in strained ferroelectric PbTiO 3 films

Nanoscale ferroelectrics are expected to exhibit various exotic domain configurations, such as the full flux-closure pattern that is well known in ferromagnetic materials. Here we observe not only the atomic morphology of the flux-closure quadrant but also a periodic array of flux closures in ferroelectric PbTiO 3 films, mediated by tensile strain on a GdScO 3 substrate. Using aberration-corrected scanning transmission electron microscopy, we directly visualize an alternating array of clockwise and counterclockwise flux closures, whose periodicity depends on the PbTiO 3 film thickness. In the vicinity of the core, the strain is sufficient to rupture the lattice, with strain gradients up to 10 9 per meter. We found engineering strain at the nanoscale may facilitate the development of nanoscale ferroelectric devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Symmetry breaking and electrical frustration during tip-induced polarization switching in the non-polar cut of lithium niobate single crystals

Polarization switching in ferroelectric materials is governed by a delicate interplay between bulk polarization dynamics and screening processes at surfaces and domain walls. Here we explore the mechanism of tip-induced polarization switching in the non-polar cuts of uniaxial ferroelectrics. In this case, in-plane component of polarization vector switches, allowing for detailed observations of resultant domain morphologies. We observe surprising variability of resultant domain morphologies stemming from fundamental instability of formed charged domain wall and associated electric frustration. In particular, we demonstrate that controlling vertical tip position allows the polarity of the switching to be controlled. This represents very unusual form of symmetry breaking where mechanical motion in vertical direction controls the lateral domain growth. The implication of these studies for ferroelectric devices and domain wall electronics are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Humidity effects on tip-induced polarization switching in lithium niobate

In the last several decades, ferroelectrics have attracted much attention as perspective materials for nonlinear optics and data storage devices. Scanning probe microscopy (SPM) has emerged as a powerful tool both for studies of domain structures with nanoscale spatial resolution and for writing the isolated nanodomains by local application of the electric field. Quantitative analysis of the observed behavior requires understanding the role of environmental factors on imaging and switching process. Here, we study the influence of the relative humidity in the SPM chamber on tip-induced polarization switching. The observed effects are attributed to existence of a water meniscus between the tip and the sample surface in humid atmosphere. These results are important for a deeper understanding of complex investigations of ferroelectric materials and their applications and suggest the necessity for fundamental studies of electrocapillary phenomena at the tip-surface junction and their interplay with bias-induced materials responses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗