Speaker
Prof.
Gustau Catalan
(ICREA and ICN2)
Description
Bending a dielectric material of any symmetry generates polarization thanks to the so-called flexoelectric effect. Conversely, applying a voltage to a dielectric material will cause it to bend spontaneously, due to the converse (or inverse) flexoelectric effect. Both direct and inverse flexoelectricity scale up with the inverse of the thickness of the material, so this phenomenon is gaining prominence with the advent of nanotechnology. On the other hand, and despite its surge in popularity, there have been –until recently- enormous gaps in our knowledge about flexoelectricity, including such fundamental questions as the actual order of magnitude of the intrinsic flexoelectric coefficients, the role of surfaces in the total flexoelectric performance, or even whether flexoelectricity can only happen in insulators.
Seeking to answer these questions, the PhD project of Jackeline Narváez has studied the flexoelectricity of single crystals. Her results resolve previous controversies by establishing that (i) the intrinsic flexoelectric coefficients of even the best flexoelectric materials does not exceed a few nC/m; (ii) in relaxors (and some ferroelectrics), there are additional contributions from polar nanodomains that can elevate the total flexoelectric coefficient to the µC/m range; (iii) the contribution of surfaces is at least as big –and sometimes bigger- as intrinsic bulk flexoelectricity and, contrary to previously thought, it is (at least indirectly) measurable, and (iv) semiconductors can also be flexoelectric, and moreover their flexoelectric coefficients can reach the mC/m range; this is one million times more than the intrinsic flexoelectricity of dielectric insulators.
In my talk, I will give an overview of the field of flexoelectricity and a summary of the main results (contextualzing their significance) from the PhD thesis of Jackeline Narvaez, ex-aequo winner of the GEFES award to the best thesis in experimental condensed matter physics.
Primary author
Prof.
Gustau Catalan
(ICREA and ICN2)
Co-author
Dr.
Jackeline Narvaez
(Universidad de los Andes)
