News Description

Prof. Gustau Catalan from Institut Catala de Nanotecnologia (ICN), Bellaterra, Spain, will visit us on October 1st.
He is going to give a seminar on Flexoelectricity at 10:00 a.m. in Shannon room (1st floor of Maxwell building).

Flexoelectricity: Strain vs Strain Gradients in Ferroelectrics

All ferroelectrics are piezoelectric and therefore display a strong intrinsic coupling between deformation (strain) and polarization. When growing ferroelectric thin films onto different substrates, the substrate-induced mismatch strain imposed modifies the ferroelectricity of the films; this is known as “strain engineering” and it is a highly effective tool to tune the ferroelectricity of thin films. However, although homogeneous strain can change the magnitude of polarization, it cannot change its sign. Control over polarity can instead be achieved through the linear coupling between polarization and strain gradients, a phenomenon known as “flexoelectricity”.

Flexoelectricity is a higher order coupling than piezoelectricity, and thus generally a smaller effect, but it grows in inverse proportion to lengthscale: at the nanoscale, gradients can be large enough for flexoelectricity to be the dominant effect. This offers new functional possibilities that may be exploited, such as the possibility of writing ferroelectric memories using pure mechanical pressure. The basic physics of flexoelectricity, and some recent examples illustrating its importance at the nanoscale, will form the basis of this talk.

REFERENCES
1.    H. Lu, C.-W. Bark, D. Esque de los Ojos, J. Alcala, C. B. Eom, G. Catalan, A. Gruverman,  Mechanical Writing of Ferroelectric Polarization, Science 336, 59-61 (2012).
2.    G. Catalan, A. Lubk, A. H. G. Vlooswijk, E. Snoeck, C. Magen, A. Janssens, G. Rispens, G. Rijnders, D. H. A. Blank and B. Noheda; Flexoelectric rotation of polarization in ferroelectric thin films, Nature Materials 10, 963 (2011).