18 Oct 2011 - Ultra-thin piezoelectrics for energy harvesting

Piezoelectric materials can transform mechanical energy into electrical energy and vice versa. Because of that they are used in a multitude of everyday applications from gas lighters to inkjet printers and from ultrasound generators in medical applications (echography devices, blood sensors, lithotripters) to vibration dampers (in cars, skis, helicopter blade).

However, piezoelectric materials have the potential to play an even greater role in society by harvesting the energy that is wasted ubiquitously as vibrations (from cars, house appliances, industrial machine) and transforming it into electricity. But in order to fulfill our dream of paving roads, railways and homes with piezoelectrics, these materials have to be made lighter, thinner and less toxic than the ones available today (which contain heavy chemical elements). An important step into this direction has been achieved by a collaboration between Beatriz Noheda (RUG, Zernike Institute for Advanced Materials), Guus Rijnders and co-workers (IMS, Mesa+ Institute for Nanotechnology, University of Twente), the CIN2-Barcelona and the CEMES-CNRS Institutes in Toulouse and Zaragoza. The results have been published in Nature Materials.

Flexoelectricity

The researches have shown that ultra-thin films (with thickness of about 100 atomic layers) of piezoelectric materials deposited under carefully designed conditions, self-organize and flex at the nanometer scale in periodic fashion. This produces huge strain gradients (large differences in the distances between atoms) in such a way that a new mechanism to produce piezoelectricity can take place (so-called flexoelectricity). This greatly increases the materials response at these small thicknesses. Moreover, this novel way of producing piezoelectricity is less dependent on the chemical composition and will allow non-toxic and more readily available materials to be investigated for piezoelectric energy harvesting application.

Map of the X-ray diffraction intensity measured in the flexed ultra-thin films, showing periodic self-organization and unusually large strain gradients.

Reference: Flexoelectric rotation of polarization in ferroelectric thin films, 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. Nature Materials.
DOI: http://dx.doi.org/10.1038/NMAT3141