arXiv subjects

Iuliia Kiseleva

Publications and source records attributed to Iuliia Kiseleva.

7 recordsLinked to original sources

arXiv2026

Uniaxial strain-driven ferroelastic domain control in LaAlO3

Multiferroic domain walls in functional oxides exhibit properties distinct from the bulk and are increasingly exploited as active elements in nanoelectronic and photonic devices. Deterministic control of domain populations has typically remained limited to local control, or removal with temperature. Here we demonstrate continuous, reversible manipulation of the ferroelastic domain structure in single-crystal LaAlO$_3$ using in-situ uniaxial strain. Combining atomic force microscopy, X-ray diffraction, and Raman spectroscopy with first-principles calculations we map the complete microscopic evolution of the twin domain population through the strain-driven transition from the rhombohedral $R\bar{3}c$ ground state toward the predicted orthorhombic $Fmmm$ phase. Applied strains below $0.5\%$ produce pronounced surface flattening and large-scale domain reorganisation, establishing uniaxial strain as a technically accessible control parameter for ferroelastic domain engineering. These results open a route to active, real-time programming of domain architectures in LaAlO$_3$-based heterostructures, with implications for strain-tunable superconducting interfaces, nanoscale phonon-polariton optics, and ultrafast lattice control.

cond-mat.mtrl-sci↗

arXiv2026

The domain-wall/metal-electrode injection barrier in lithium niobate: Which electrical transport model fits best?

The comprehensive description of both the electrical transport along conductive domain walls (CDWs) in lithium niobate (LNO) single crystals and the charge injection at the interfacing metal electrodes, emerged to be a complex challenge. Recently, a heuristic evaluation allowed to postulate the "R2D2" equivalent-circuit model (consisting of two parallel resistor-diode pairs) to appropriately match the DC current-voltage (I-V) characteristics. Here, we carefully revisit the interfacial electrical behavior, i.e., the diode part of the equivalent circuit model, since many more processes beyond the diode-related electron hopping transport (HT) assumed so far, may concurrently occur, such as thermionic emission (TE), Fowler-Nordheim tunneling (FNT), space-charge limited conduction (SCLC), and others more. The "R2D2" model thus needs to be generalized into an "R2X2" circuit model (with X = HT, TE, FNT, and others) to fit to the experimental data. Moreover, to double check for the best I-V curve fitting to the different theories, we apply a higher-harmonic DW current-contribution (HHCC) analysis, i.e., an AC I-V inspection, that allows us to discriminate between all these possible models with much higher precision than from pure DC I-V curve fitting. Both the AC and DC analysis reveal well consistent results, finally finding that the FNT model accounts best for the domain-wall/electrode junctions investigated here.

cond-mat.mtrl-sci↗

arXiv2025

Demonstration of domain wall current in MgO-doped lithium niobate single crystals up to 400 °C

Conductive ferroelectric domain walls (DWs) represent a promising topical system for the development of nanoelectronic components and device sensors to be operational at elevated temperatures. DWs show very different properties as compared to their hosting bulk crystal, in particular with respect to the high local electrical conductivity. The objective of this work is to demonstrate DW conductivity up to temperatures as high as \SI{400}{\degreeCelsius} which extends previous studies significantly. Experimental investigation of the DW conductivity of charged, inclined DWs is performed using \SI{5}{\mole\percent} MgO-doped lithium niobate single crystals. \CR{Current-voltage (\IV) curves are determined by DC electrometer measurements and impedance spectroscopy and found to be identical. Moreover, impedance spectroscopy enables to recognize artifacts such as damaged electrodes. Temperature dependent measurements} over repeated heating cycles reveal two distinct thermal activation energies for a given DW, with the higher of the activation energies only measured at higher temperatures. Depending on the specific sample, the higher activation energy is found above \SI{160}{\degreeCelsius}~to~\SI{230}{\degreeCelsius}. This suggests, in turn, that more than one type of defect/polaron is involved, and that the dominant transport mechanism changes with increasing temperature. First principles atomistic modelling suggests that the conductivity of inclined domain walls cannot be solely explained by the formation of a 2D carrier gas and must be supported by hopping processes. This holds true even at temperatures as high as \SI{400}{\degreeCelsius}. Our investigations underline the potential to extend \DWC based nanoelectronic and sensor applications even into the so-far unexplored temperature range up to \SI{400}{\degreeCelsius}.

physics.app-ph↗

arXiv2025

In-situ SHG microscopy investigation of the domain-wall-conductivity enhancement procedure in lithium niobate

Conductive domain walls (CDWs) in the uniaxial ferroelectric lithium niobate (LiNbO$_3$, LN) have attracted a lot of interest as potential elements in 2D nanoelectronics, due to their orders-of-magnitude larger electronic AC and DC conductivities as compared to the host material. On the way towards generating standardized CDWs into z-cut bulk LN crystals with controllable geometry and electrical properties, we have encountered setbacks recently: Although the first preparation step, i.e., the established UV-light-assisted liquid-electrode poling, reliably creates fully penetrating hexagonal domains with the DWs being aligned almost parallel to the polarization axis, the second step in the DW 'conductivity-enhancement' process through post-growth voltage ramping, resulted in randomly-shaped DWs as reflected in their different current-voltage (I-V) characteristics even after having applied the same process parameters. To clarify this phenomenon, we present here an \textit{in-situ} and time-resolved second-harmonic-generation (SHG) microscopy investigation of DW samples of different sizes, monitoring the DW evolution during that critical voltage ramping, which allowed us to reconstruct the 3D DW shapes both prior to and after the enhancement process. As a result, we are able to map the temporal changes of the local DW inclination angle $α$, and to quantify the DW velocity. As a consequence, we need to re-assess and re-think the origin of the DW conductivity (DWC) in LN: The hitherto assumed simple connection between $α$ and the DWC can not be generalized, since point defects accumulating along DWs act as extra sources for charge carrier trapping/release, significantly contributing to the DW current.

cond-mat.mtrl-sci↗

arXiv2024

Probing Ferroelectric Phase Transitions in Barium Titanate Single Crystals via $\it{in-situ}$ Second Harmonic Generation Microscopy

Ferroelectric materials play a crucial role in a broad range of technologies due to their unique properties that are deeply connected to the pattern and behavior of their ferroelectric (FE) domains. Chief among them, barium titanate (BaTiO$_3$; BTO) sees widespread applications such as in electronics but equally is a ferroelectric model system for fundamental research, e.g., to study the interplay of such FE domains, the domain walls (DWs), and their macroscopic properties, owed to BTO's multiple and experimentally accessible phase transitions. Here, we employ Second Harmonic Generation Microscopy (SHGM) to $\it{in-situ}$ investigate the cubic-to-tetragonal (at $\sim$126$^\circ$C) and the tetragonal-to-orthorhombic (at $\sim$5$^\circ$C) phase transition in single-crystalline BTO via 3-dimensional (3D) DW mapping. We demonstrate that SHGM imaging provides the direct visualization of FE domain switching as well as the domain dynamics in 3D, shedding light on the interplay of the domain structure and the phase transition. These results allow us to extract the different transition temperatures locally, to unveil the hysteresis behavior, and to determine the type of phase transition at play (1st/2nd order) from the recorded SHGM data. The capabilities of SHGM in uncovering these crucial phenomena can easily be applied to other ferroelectrics to provide new possibilities for $\it{in-situ}$ engineering of advanced ferroic devices.

cond-mat.mtrl-sci↗

arXiv2024

Towards the reproducible fabrication of conductive ferroelectric domain walls into lithium niobate bulk single crystals

Ferroelectric domain walls (DWs) are promising structures for assembling future nano-electronic circuit elements on a larger scale, since reporting domain wall currents of up to 1 mA per single DW. One key requirement hereto is their reproducible manufacturing by gaining preparative control over domain size and domain wall conductivity (DWC). To date, most works on DWC have focused on exploring the fundamental electrical properties of individual DWs within single shot experiments, with emphasis on quantifying the origins for DWC. Very few reports exist when it comes to compare the DWC properties between two separate DWs, and literally nothing exists where issues of reproducibility in DWC devices have been addressed. To fill this gap while facing the challenge of finding guidelines achieving predictable DWC performance, we report on a procedure that allows us to reproducibly prepare single hexagonal domains of a predefined diameter into uniaxial ferroelectric (FE) lithium niobate (LN) single crystals of 200 and 300 micrometers thickness, respectively. We show that the domain diameter can be controlled with an error of a few percent. As-grown DWs are then subjected to a standard procedure of current-controlled high-voltage DWC enhancement, repetitively reaching a DWC increase of 6 orders of magnitude. While all resulting DWs show significantly enhanced DWC values, subtle features in their individual current-voltage (I-V) characteristics hint towards different 3D shapes into the bulk, with variations probably reflecting local heterogeneities by defects, DW pinning, and surface-near DW inclination, which seem to have a larger impact than expected.

cond-mat.mtrl-sci↗

arXiv2023

R2D2 -- An equivalent-circuit model that quantitatively describes domain wall conductivity in ferroelectric LiNbO$_3$

Ferroelectric domain wall (DW) conductivity (DWC) can be attributed to two separate mechanisms: (a) the injection/ejection of charge carriers across the Schottky barrier formed at the (metal-) electrode-DW junction and (b) the transport of those charge carriers along the DW. Current-voltage (IU) characteristics, recorded at variable temperatures from LiNbO$_3$ (LNO) DWs, are clearly able to differentiate between these two contributions. Practically, they allow us here to directly quantify the physical parameters relevant for the two mechanisms (a) and (b) mentioned above. These are, e.g., the resistance of the DW, the saturation current, the ideality factor, and the Schottky barrier height of the electrode/DW junction. Furthermore, the activation energies needed to initiate the thermally-activated electronic transport along the DWs, can be extracted. In addition, we show that electronic transport along LiNbO$_3$ DWs can be elegantly viewed and interpreted in an adapted semiconductor picture based on a double-diode/double-resistor equivalent circuit model, the R2D2 model. Finally, our R2D2 model was checked for its universality by fitting the DWC data not only to z-cut LNO bulk DWs, but equally to z-cut thin-film LNO DWs, and DWC from x-cut DWs as reported in literature.

cond-mat.mtrl-sci↗