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Flexoelectricity at the nanoscale: switchable mechanical properties of ferroelectrics

AuthorsCordero-Edwards, Kumara; Abdollahi, A.; Domingo, Neus ; Sort, J.; Catalán, Gustau
Issue Date2016
PublisherCSIC-ICN Centro de Investigación en Nanociencia y Nanotecnología (CIN2)
CitationFuerzas y Túnel (2016)
AbstractElectrical and mechanical stimulus induced by the tip of an Atomic Force Microscope (AFM) is the basis for the generation and detection of different types of phenomenologies; from imaging ferroelectric ordering of thin films or single crystals to piezoelectric characterization. Moreover, AFM tip can generate flexoelectric fields which can be applied to mechanical writing of ferroelectric polarization. The mechanical properties of materials are believed to be invariant with respect to space inversion, even for non-centrosymmetric materials, such as ferroelectrics, because all the magnitudes involved (stress, strain, and elastic constants) are described by even parity tensors. The standard theory, however, does not take into account the effect of flexoelectricity on structural properties. Flexoelectricity is a coupling between polarization and strain gradients, and it can be huge around crack tips, so it should be important in fracture phenomena. Our recent work, using the nanoindentation technique and PFM images, provide evidences that this spatial inversion symmetry is broken in ferroelectric materials. In this presentation, I will give an overview on flexoelectric induced effects in PFM. I will show how the nanoindentation technique enables us to mobilize the flexoelectric effect around the sharp indenter tip while simultaneously probing the mechanical properties of the material. The measurements on a stoichiometric single crystal Lithium Niobate (SLN) and a periodic poled Lithium Niobate (PPLN) indicate that the energy dissipation, fracture toughness, and mechanical properties are asymmetric in respect to the sign of the polarization. The PFM images of the indented areas show domain switching in positively poled regions, resulting in different polarization patterns in 180 antiparallel domains. We show that this new physical phenomenon is enabled by the interplay between ferroelectricity and flexoelectricity. Aside from the fundamental importance of this new insight, the predicted asymmetry may also find uses in smart nanodevices and coatings with switchable mechanical properties. Finally, I will also give evidences of inverse flexoelectric effects as induced by the strong electric field gradients emanating from a sharp PFM tip, which are present in the measurements performed in all dielectric materials.
DescriptionResumen del póster presentado a la 10th Conferencia Fuerzas y Túnel, celebrada en Girona (España) del 5 al 7 de septiembre de 2016.
Appears in Collections:(CIN2) Comunicaciones congresos
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