Staff directory
Rohini Kumara Cordero Eduards
Senior Postdoctoral Researcher
kumara.cordero(ELIMINAR)@icn2.cat
Oxide Nanophysics
- ORCID: 0000-0003-3721-7863
Publications
2023
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Translational Boundaries as Incipient Ferrielectric Domains in Antiferroelectric PbZrO3
Liu, Y; Niu, RM; Majchrowski, A; Roleder, K; Cordero-Edwards, K; Cairney, JM; Arbiol, J; Catalan, G Physical Review Letters; 130 (21): 216801. 2023. 10.1103/PhysRevLett.130.216801. IF: 8.600
2021
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Mechanical reading of ferroelectric polarization
Stefani C., Langenberg E., Cordero-Edwards K., Schlom D.G., Catalan G., Domingo N. Journal of Applied Physics; 130 (7, 0059930) 2021. 10.1063/5.0059930. IF: 2.546
Flexoelectricity is a property of dielectric materials whereby they exhibit electric polarization induced by strain gradients; while this effect can be negligible at the macroscale, it can become dominant at the nanoscale, where strain gradients can turn out to be tremendous. Previous works have demonstrated that flexoelectricity coupled with piezoelectricity enables the mechanical writing of ferroelectric polarization. When considering ferroelectric materials with out-of-plane polarization, the coupling of piezoelectricity with flexoelectricity can insert a mechanical asymmetry to the system and enable the distinction of oppositely polarized domains, based on their nanomechanical response. Using atomic force microscopy and, more specifically, contact resonance techniques, the coupling of flexoelectricity to piezoelectricity can be exploited to mechanically read the sign of ferroelectric polarization in a non-destructive way. We have measured a variety of ferroelectric materials, from a single crystal to thin films, and domains that are polarized down always appear to be stiffer than oppositely polarized domains. In this article, we demonstrate experimentally that the phenomenon is size-dependent and strongly enhanced when the dimension of the material is reduced to nanoscale in thin films. Ultimately, we demonstrate how the sensitivity in mechanical reading of ferroelectric polarization can be improved by appropriately tuning the mechanical stiffness of the cantilevers. © 2021 Author(s).
2019
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Flexoelectric Fracture-Ratchet Effect in Ferroelectrics
Cordero-Edwards K., Kianirad H., Canalias C., Sort J., Catalan G. Physical Review Letters; 122 (13, 135502) 2019. 10.1103/PhysRevLett.122.135502. IF: 9.227
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 is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model. © 2019 American Physical Society.
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Surface charged species and electrochemistry of ferroelectric thin films
Domingo N., Gaponenko I., Cordero-Edwards K., Stucki N., Pérez-Dieste V., Escudero C., Pach E., Verdaguer A., Paruch P. Nanoscale; 11 (38): 17920 - 17930. 2019. 10.1039/c9nr05526f. IF: 6.970
The combination of scanning probe microscopy and ambient pressure X-ray photoelectron spectroscopy opens up new perspectives for the study of combined surface chemical, electrochemical and electromechanical properties at the nanoscale, providing both nanoscale resolution of physical information and the chemical sensitivity required to identify surface species and bulk ionic composition. In this work, we determine the nature and evolution over time of surface chemical species obtained after water-mediated redox reactions on Pb(Zr0.2,Ti0.8)O3 thin films with opposite as-grown polarization states. Starting with intrinsically different surface chemical composition on the oppositely polarized films (as a result of their ferroelectric-dominated interaction with environmental water), we identify the reversible and irreversible electrochemical reactions under an external electric field, distinguishing switching and charging events. We find that while reversible ionic displacements upon polarization switching dominate screening in the bulk of the sample, polarization dependent irreversible redox reactions determine surface chemical composition, which reveals itself as a characteristic fingerprint of the ferroelectric polarization switching history. © 2019 The Royal Society of Chemistry.
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Water adsorption, dissociation and oxidation on SrTiO 3 and ferroelectric surfaces revealed by ambient pressure X-ray photoelectron spectroscopy
Domingo N., Pach E., Cordero-Edwards K., Pérez-Dieste V., Escudero C., Verdaguer A. Physical Chemistry Chemical Physics; 21 (9): 4920 - 4930. 2019. 10.1039/c8cp07632d. IF: 3.567
Water dissociation on oxides is of great interest because its fundamental aspects are still not well understood and it has implications in many processes, from ferroelectric polarization screening phenomena to surface catalysis and surface chemistry on oxides. In situ water dissociation and redox processes on metal oxide perovskites which easily expose TiO 2 -terminated surfaces, such as SrTiO 3 , BaTiO 3 or Pb(Zr,Ti)O 3 , are studied by ambient pressure XPS, as a function of water vapour pressure. From the analysis of the O1s spectrum, we determine the presence of different types of oxygen based species, from hydroxyl groups, either bound to Ti 4+ and metal sites or lattice oxygen, to different peroxide compounds, and propose a model for the adsorbate layer composition, valid for environmental conditions. From the XPS analysis, we describe the existing surface redox reactions for metal oxide perovskites, occurring at different water vapour pressures. Among them, peroxide species resulting from surface oxidative reactions are correlated with the presence of Ti 4+ ions, which are observed to specifically promote surface oxidation and water dissociation as compared to other metals. Finally, surface peroxidation is enhanced by X-ray beam irradiation, leading to a higher coverage of peroxide species after beam overexposure and by ferroelectric polarization, demonstrating the enhancement of the reactivity of the surfaces of ferroelectric materials due to the effect of internal electric fields. © 2019 the Owner Societies.