Atomic-scale investigations and electro-mechanical properties of ferroelectric ceramics with polar nano-regions

The macroscopic dielectric, piezoelectric and anelastic responses of ferroelectric and relaxor materials are in general strongly dominated by the dynamics of polar nano-regions and ferroelectric domain walls. While there has... [ view full abstract ]

The macroscopic dielectric, piezoelectric and anelastic responses of ferroelectric and relaxor materials are in general strongly dominated by the dynamics of polar nano-regions and ferroelectric domain walls. While there has been a significant progress over the last decade in understanding the structure and properties of domain walls, there is presently no consensus on structure of polar regions in relaxors, relaxor-ferroelectric solid solutions and in paraelectric phase of ferroelectrics. Even very existence of polar nano-regions has sometimes been questioned. Clearly, this complex problem requires a comprehensive approach where composition, structure and dynamics of polar regions are investigated on atomic, mesoscopic and macroscopic scales and where theoretical models are validated by the entire set of experimental observations.

We report on results of (i) atomic scale investigation of the structure of polar regions in paraelectric phase of perovskite (Ba_0.60Sr_0.40)TiO₃ ceramics and (ii) a study of piezoelectric, anelastic and nonlinear dielectric properties of this and related (Ba,Sr)TiO₃ materials. HRSTEM observations imply that the expected cubic symmetry of the investigated samples is broken on nanoscale. The symmetry of the polar regions is likely lower than that of the successive ferroelectric phases of this material. The measurements of the dielectric nonlinearity indicate similarities with canonical relaxor Pb(Mg_1/3Nb_2/3)O₃ although investigated samples of (Ba_0.60Sr_0.40)TiO₃ do not exhibit relaxor characteristics.

Broader implications of these results are discussed.