Michael Roth

Abstract:

The acoustic emission (AE) method, in conjunction with the dielectric measurements, has been used to study phase transitions in numerous ceramic and single crystalline relaxor ferroelectrics, such as the prototypical Pb(Zn1/3Nb2/3)O3 and Pb(Mg1/3Nb2/3)O3 perovskite compounds and their solid solutions with PbTiO3. Common features related to the critical conditions responsible for the giant piezoelectric and electromechanical responses in all relaxor systems have been studied. The extraordinary properties have been revealed at critical points in the X-T-E (composition-temperature-electric field) phase diagrams of the compounds studied, being related to the existence polar nanoregions (PNRs). We have found that the critical electric fields in relaxor ferroelectrics correspond to maximal AE activity at minimum values of the diffuse thermal dielectric permittivity peaks. A combined investigation of the critical phenomena comprising the AE, dielectric spectroscopy, in situ Raman scattering and time-resolved synchrotron XRD structural analysis has been carried out to the origin of the giant piezoelectricitiy. The primary types and driving mechanisms behind the PNR atomic clustering associated with the critical behavior have been revealed. Some applications of relaxor ferroelectrics as candidate materials for broadband and high-sensitivity ultrasonic transducers and sensors is discussed as well.