Electric field effect on polar nanoregions of uniaxial ferroelectric SrxBa1−xNb2O6 with weak random fields studied by Brillouin scattering

Abstract

The electric field effects on the acoustic properties of uniaxial ferroelectric SrxBa1−xNb2O6 (x = 0.40, SBN40) crystals with weak random fields were studied by Brillouin scattering. On field cooling, the minimum of longitudinal acoustic (LA) velocity shifted to a higher value and a marked increase in LA velocity was observed below the Curie temperature TC. This signifies the enhancement of the long-range ferroelectric order due to the alignment of polar nanoregions (PNRs) along the field direction. After poling the crystal with a high electric field for 60 min above TC, the alignment of all PNRs along the field direction was observed. By decreasing the poling time, LA mode splitting was observed below TC owing to the back switching of PNRs. In a field-dependent measurement below TC, a mixed state consisting of macro- and nanodomains persisted up to a very high electric field because of the incomplete switching of nanodomains due to the interaction among PNRs.