Piezoelectricity and local structural distortions in (Na_(0.5)Bi_(0.5))_(1-x)Sr_x TiO_3-Bi_(12)TiO_(20) flexoelectric-type polar ceramics

摘要

We have previously described sintered Na_(0.5)Bi_(0.5)TiO_3-Bi_(12)TiO_(20) composites as flexoelectric-type polar ceramics because they have a net macroscopic flexoelectric polarization. Here, we report on the universal existence of the macroscopic flexoelectric polarization in the (Na_(0.5)Bi_(0.5))_(1-x)Sr_x TiO_3-Bi_(12)TiO_(20) system, in which enhanced piezoelectricity is observed. By combining Raman spectroscopy and x-ray photoelectron spectroscopy techniques, we have identified the local flexoelectric polarization as distorted BiO_5 polyhedra and TiO_6, octahedra in the SrTiO_3-Bi_(12)TiO_(20)o ceramic. The macroscopic polarization may be due to the partial alignment of these distorted units located within the grain boundary amorphous phases. Bi_(12)TiO_(20) could have an important role in these flexoelectric-type polar ceramics.