arXiv subjects

Neus Domingo

Publications and source records attributed to Neus Domingo.

7 recordsLinked to original sources

arXiv2026

Absence of lateral domain wall mobility in Zn1-xMgxO thin films

Polarization reversal in ferroelectrics arises from the coupled processes of domain nucleation and subsequent growth, yet the governing mechanisms differ fundamentally between classical perovskite oxides and emerging wurtzite ferroelectrics. While switching in perovskites is typically governed by mobile domain walls whose field-driven propagation dominates macroscopic kinetics, here we show that polarization reversal in wurtzite Zn1-xMgxO proceeds through a qualitatively different pathway. Using scanning oscillator microscopy, in combination with point pulse-imaging methods, we directly map local switching events and domain wall responses, revealing that domain walls in Zn1-xMgxO exhibit negligible lateral mobility (sub 10nm) and that polarization reversal proceeds predominantly through the nucleation of vertically extended columnar filaments with a lateral size on the order of the grains. This nucleation-controlled switching contrasts sharply with the growth-mediated dynamics characteristic of perovskite ferroelectrics and explains the abrupt, spatially localized switching behavior observed in wurtzite systems. These results establish nucleation-dominated filamentary reversal as a defining switching mechanism in Zn1-xMgxO and point towards the need for further studies to understand correlation lengths and nucleation processes across a range of grain sizes.

cond-mat.mtrl-sci↗

arXiv2024

Hierarchical domain structures in buckled ferroelectric free sheets

Flat elastic sheets tend to display wrinkles and folds. From pieces of clothing down to two-dimensional crystals, these corrugations appear in response to strain generated by sheet compression or stretching, thermal or mechanical mismatch with other elastic layers, or surface tension. Extensively studied in metals, polymers and, more recently, in van der Waals exfoliated layers, with the advent of thin single crystal freestanding films of complex oxides, researchers are now paying attention to novel microstructural effects induced by bending ferroelectric-ferroelastics, where polarization is strongly coupled to lattice deformation. Here we show that wrinkle undulations in BaTiO3 sheets bonded to a viscoelastic substrate transform into a buckle delamination geometry when transferred onto a rigid substrate. Using spatially resolved techniques at different scales (Raman, scanning probe and electron microscopy), we show how these delaminations in the free BaTiO3 sheets display a self-organization of ferroelastic domains along the buckle profile that strongly differs from the more studied sinusoidal wrinkle geometry. Moreover, we disclose the hierarchical distribution of a secondary set of domains induced by the misalignment of these folding structures from the preferred in-plane crystallographic orientations. Our results disclose the relevance of the morphology and orientation of buckling instabilities in ferroelectric free sheets, for the stabilization of different domain structures, pointing to new routes for domain engineering of ferroelectrics in flexible oxide sheets.

cond-mat.mtrl-sci↗

arXiv2021

Deconvolution of phonon scattering by ferroelectric domain walls and point defects in a PbTiO3 thin film deposited in a composition-spread geometry

We present a detailed analysis of the temperature dependence of the thermal conductivity of a ferroelectric PbTiO3 thin film deposited in a composition-spread geometry enabling a continuous range of compositions from ~25% titanium-deficient to ~20% titanium-rich to be studied. By fitting the experimental results to the Debye model we deconvolve and quantify the two main phonon scattering sources in the system: ferroelectric domain walls (DWs) and point defects. Our results prove that ferroelectric DWs are the main agent limiting the thermal conductivity in this system, not only in the stoichiometric region of the thin film ([Pb]/[Ti]~1), but also when the concentration of cation point defects is significant (up to ~15%). Hence, DWs in ferroelectric materials are a source of phonon scattering at least as effective as point defects. Our results demonstrate the viability and effectiveness of using reconfigurable DWs to control the thermal conductivity in solid-state devices.

cond-mat.mtrl-sci↗

arXiv2020

Local and correlated studies of humidity-mediated ferroelectric thin film surface charge dynamics

Electrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr$_{0.2}$Ti$_{0.8}$)O$_3$ thin films. We analyze the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorization, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh-Nagumo reaction-diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis.

cond-mat.mtrl-sci↗

arXiv2020

Ferroelectric 180 degree walls are mechanically softer than the domains they separate

Domain walls are functionally different from the domains they separate, but little is known about their mechanical properties. Using scanning probe microscopy, we have measured the mechanical response of ferroelectric 180o domain walls and observed that, despite separating domains that are mechanically identical (non-ferroelastic), the walls are mechanically distinct -- softer -- compared to the domains. This effect has been observed in different ferroelectric materials (LiNbO3, BaTiO3, PbTiO3) and with different morphologies (from single crystals to thin films) so it appears to be universal. We propose a theoretical framework that explains the domain wall softening and justifies that the effect should be common to all ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2019

Periodicity doubling cascades: direct observation in ferroelastic materials

Very sensitive responses to external forces are found near phase transitions. However, phase transition dynamics and pre-equilibrium phenomena are difficult to detect and control. We have directly observed that the equilibrium domain structure following a phase transition in BaTiO3, a ferroelectric and ferroelastic material, is attained by halving of the domain periodicity, sequentially and multiple times. The process is reversible, displaying periodicity doubling as temperature is increased. This observation is backed theoretically and can explain the fingerprints of domain period multiplicity observed in other systems, strongly suggesting this as a general model for pattern formation during phase transitions in ferroelastic materials.

cond-mat.mtrl-sci↗

arXiv2015

Giant reversible nanoscale piezoresistance at room temperature in Sr2IrO4 thin films

Layered iridates have been the subject of intense scrutiny on account of their unusually strong spin-orbit coupling, which opens up a narrow gap in a material that would otherwise be a metal. This insulating state is very sensitive to external perturbations. Here, we show that vertical compression at the nanoscale, delivered using the tip of a standard scanning probe microscope, is capable of inducing a five orders of magnitude change in the room temperature resistivity of Sr2IrO4. The extreme sensitivity of the electronic structure to anisotropic deformations opens up a new angle of interest on this material, and the giant and fully reversible perpendicular piezoresistance makes iridates a promising material for room temperature piezotronic devices.

cond-mat.mtrl-sci↗