Breaking of macroscopic centric symmetry in paraelectric phases of ferroelectric materials and implications for flexoelectricity.
A centrosymmetric stress cannot induce a polar response in centric materials; piezoelectricity is, for example, possible only in non-centrosymmetric structures. An exception is metamaterials with shape asymmetry, which may be polarized by stress even when the material is centric. In this case the mechanism is flexoelectricity, which relates polarization to a strain gradient. The flexoelectric response scales inversely with size, thus a large effect is expected in nanoscale materials. Recent experiments in polycrystalline, centrosymmetric perovskites (for example, (Ba, Sr)TiO3) have indicated values of flexoelectric coefficients that are orders of magnitude higher than theoretically predicted, promising practical applications based on bulk materials. We show that materials with unexpectedly large flexoelectric response exhibit breaking of the macroscopic centric symmetry through inhomogeneity induced by the high-temperature processing. The emerging electro-mechanical coupling is significant and may help to resolve the controversy surrounding the large apparent flexoelectric coefficients in this class of materials.
Ceramics Laboratory, Swiss Federal Institute of Technology in Lausanne-EPFL, 1015 Lausanne, Switzerland.
Alberto
A
Biancoli
Department of Materials Science and Engineering, North Carolina State University Raleigh, North Carolina 27695, USA.
Chris M
CM
Fancher
Department of Materials Science and Engineering, North Carolina State University Raleigh, North Carolina 27695, USA.
Jacob L
JL
Jones
Ceramics Laboratory, Swiss Federal Institute of Technology in Lausanne-EPFL, 1015 Lausanne, Switzerland.
Dragan
D
Damjanovic