Nanostructuring effects in piezoelectric BiScO 3- PbTiO 3 ceramics

The apparent contradiction between the persistence of the polar state in morphotropic phase boundary BiScO3-PbTiO3 at the nanoscale, and the vanishing of the macroscopic ferroelectric switching and of the dielectric anomaly associated with the ferroelectric phase transition in nanostructured ceramics is solved. Raman spectroscopy results unambiguously demonstrate that the same polar phase exists in coarse grained and nanostructured materials. Soft modes were identified and followed upon heating, which allowed transition temperatures to be estimated. A shift of only 60°C was established as the size effect down to 24 nm average sized grains. Impedance spectroscopy was used to separate grain and boundary contributions to the total electrical response. Results clearly show grain boundaries to fully dominate this response in the case of nanostructured materials, which was responsible for the vanishing of the dielectric anomaly and for a large increase in the effective coercivity, the latter resulting in the loss of functionality. This was therefore a boundary effect, liable of being recovered by boundary tailoring. Indeed, macroscopic ferroelectricity was readily uncovered when grain-boundary density was reduced by triggering grain growth.This work was funded by the Spanish former MICINN (now MINECO) through project MAT2011‐23709. Collaboration between ICMM and CEMES is framed within the COST Action MP0904. H. Amorín thanks financial support by MICINN Ramón y Cajal Programme