Nanostructuring Effects in Piezoelectric BiScO₃–PbTiO₃ Ceramics

Abstract

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.

Point defect engineering of high temperature piezoelectric BiScO3–PbTiO3 for high power operation

“…This indicates the presence of two electroactive regions that are associated with the grain bulk (low frequency process) and the grain boundaries (high frequency process). A similar result has been shown for closely related BiScO3-PbTiO3 materials [36]. The contributions of the two regions were separated by using an equivalent electric circuit to model the experimental data.…”

“…This figure is typical of electronic conduction rather than ionic, and it is proposed to be associated with hole conduction within the valence band, specifically with electron hopping between Mn 2+ and Mn 3+ at the B-site. Indeed, a similar conduction process has been described for BiScO3-PbTiO3 ceramics processed from powder synthesized by mechanochemical activation in stainless steel media [36], for which presence of Fe substituting for Sc has been described [5].…”

“…The contributions of the two regions were separated by using an equivalent electric circuit to model the experimental data. A series connection of two parallel (RQC) and (RQ) elements for the bulk and grain boundary components, respectively, was used that has been previously shown to correctly model the response of BiScO3-PbTiO3 ceramics [36]. Results Strong low-frequency dispersion was found across the temperature range where the ferroelectric transition takes place in all cases.…”

“…Exaggerated grain growth in this case decreases the coercive field down to 2.6 kV mm -1 , which is the value obtained for the fine grained unmodified material. There is thus a strong effect of grain size on coercive field, which reflects changes in the domain configuration and an increasing influence of low permittivity grain boundaries [36]. Whatever the cause is, grain size effects may hide the effect of point defects.…”

High-sensitivity piezoelectric perovskites for magnetoelectric composites

“…It has been recently shown that the grain size dependence of P r (and also d 33 ) actually reflects the increase of the effective coercitivity as the grain size decreases rather than a real decrease of the spontaneous polarization [36]. Higher electric fields would be required to approach saturation, and thus achieve an efficient poling (and a higher d 33 ) of the material.…”