arXiv subjects

Kumara Cordero-Edwards

Publications and source records attributed to Kumara Cordero-Edwards.

5 recordsLinked to original sources

arXiv2026

Domain-induced control of latent heat in freestanding BaTiO$_3$ membranes

Thin ferroelectric BaTiO$_3$ films often exhibit continuous transitions instead of the first-order behavior of bulk crystals, a discrepancy usually attributed to epitaxial strain or dimensionality. Using quasi-adiabatic nanocalorimetry on freestanding BaTiO$_3$ membranes-free of clamping and substrate heat sinking-we show that domain morphology, not thickness or boundary conditions, controls the transition order. Thick membranes with large, monodomain-like regions display clear latent heat, whereas thinner membranes with dense 180$^{\circ}$ domain patterns show a continuous transition despite undergoing the same tetragonal-cubic structural change confirmed by x-ray diffraction. Piezoresponse force microscopy links this behavior to domain-size evolution, and a Ginzburg-Landau analysis demonstrates how reduced domain size lowers the free-energy barrier, rounding a nominally first-order instability. These results identify domain morphology as the key determinant of ferroelectric transition order in oxide membranes and establish design guidelines for enhancing caloric effects through domain engineering.

cond-mat.mtrl-sci↗

arXiv2025

Beware of the water: Hidden hydrogenation of perovskite membranes made by the water-soluble sacrificial layer method

The fabrication of perovskite oxide free-standing films (membranes) by lift-off methods using water-soluble sacrificial layers is appealing because of the new mechanical degrees of freedom that these membranes present over conventional epitaxial films. However, little is known about how their fabrication process, and in particular the exposure to water during the etching step, affects their properties. Here, we investigate how membranes of two perovskite archetypes, antiferroelectric PbZrO3 and paraelectric SrTiO3, are affected by water-based etching step. Using Raman spectroscopy and X-ray diffraction, we find evidence that hydrogen penetrates the perovskite structure. Concomitant with this protonation, the functional properties also change, and both materials display ferroelectric-like behavior that is absent in bulk ceramics or hydrogen-free films at room temperature. We also find that thermal annealing can be used to expel the hydrogen from the membranes, which henceforth recover bulk-like properties. The two main conclusions of this work are that (i) any perovskite membrane made by sacrificial layer hydrolysis is vulnerable to hydrogen penetration (protonation) that can induce important but extrinsic changes in functional properties, and (ii) the hydrogen can, and should, be expelled by annealing to recover intrinsic behaviour.

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↗

arXiv2022

Switchable tribology of ferroelectrics

Artificially induced asymmetric tribological properties of ferroelectrics offer an alternative route to visualize and control ferroelectric domains. Here, we observe the switchable friction and wear behavior of ferroelectrics using a nanoscale scanning probe where down domains having lower friction coefficient than up domains can be used as smart masks as they show slower wear rate than up domains. This asymmetry is enabled by flexoelectrically coupled polarization in the up and down domains under a sufficiently high contact force. Moreover, we determine that this polarization-sensitive tribological asymmetry is universal across ferroelectrics with different chemical composition and crystalline symmetry. Finally, using this switchable tribology and multi-pass patterning with a domain-based dynamic smart mask, we demonstrate three-dimensional nanostructuring exploiting the asymmetric wear rates of up and down domains, which can, furthermore, be scaled up to technologically relevant (mm-cm) size. These findings establish that ferroelectrics are electrically tunable tribological materials at the nanoscale for versatile applications.

physics.app-ph↗

arXiv2018

Flexoelectric fracture-filter effect in ferroelectrics

The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation will be helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. This means that the theory of fracture physics can no longer assume mechanical symmetry in polar materials. The discovery of fracture asymmetry also has practical repercussions for the electromechanical fatigue of ferroelectrics and piezoelectric transducers, as well enabling a new degree of freedom for crack-based nanopatterning.

cond-mat.mtrl-sci↗