arXiv subjects

José Manuel Caicedo Roque

Publications and source records attributed to José Manuel Caicedo Roque.

3 recordsLinked to original sources

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↗

arXiv2025

Ultrafast decoupling of polarization and strain in ferroelectric BaTiO$_3$

A fundamental understanding of the interplay between lattice structure, polarization and electrons is pivotal to the optical control of ferroelectrics. The interaction between light and matter enables the remote and wireless control of the ferroelectric polarization on the picosecond timescale, while inducing strain, i.e., lattice deformation. At equilibrium, the ferroelectric polarization is proportional to the strain, and is typically assumed to be so also out of equilibrium. Decoupling the polarization from the strain would remove the constraint of sample design and provide an effective knob to manipulate the polarization by light. Here, upon an above-bandgap laser excitation of the prototypical ferroelectric BaTiO$_3$, we induce and measure an ultrafast decoupling between polarization and strain that begins within 350 fs, by softening Ti-O bonds via charge transfer, and lasts for several tens of picoseconds. We show that the ferroelectric polarization out of equilibrium is mainly determined by photoexcited electrons, instead of the strain. This excited state could serve as a starting point to achieve stable and reversible polarization switching via THz light. Our results demonstrate a light-induced transient and reversible control of the ferroelectric polarization and offer a pathway to control by light both electric and magnetic degrees of freedom in multiferroics.

cond-mat.mtrl-sci↗

arXiv2024

Photostrictive actuators based on freestanding ferroelectric membranes

Complex oxides offer a wide range of functional properties, and recent advances in fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, we demonstrate photoactuation in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent and holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light.

cond-mat.mtrl-sci↗