Electric field effect on polar nanoregions of uniaxial ferroelectric Sr_xBa_1−xNb₂O₆with 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.

Acoustic phonon anomalies in Ca doped SrTiO3quantum ferroelectrics as studied by Brillouin light scattering

“…Acoustic phonon modes were excited with a 532 nm single longitudinal mode diode pumped solid-state laser. 24,25) The incident light was focused with a 20x microscope objective on to the sample. Measurements were carried out in the FSR of 100 GHz in the temperature range of 500-90 K using a Linkam (FTIR 600) heating/cooling stage.…”

Ferroelectric phase transitions of uniaxial Sr1-xBaxNb2O6and their composition variation

“…In the TTB uniaxial ferroelectrics such as SBN40, SBN61, SBN75, CBN28, and CBN30 (Ca x Ba 1-x Nb 2 O 6 , x = 0.28 and x = 0.30), the LA mode propagating along the ferroelectric c-axis shows the minimum in the vicinity of T C . 5,8,[12][13][14][19][20][21] According to the selection rule, the TA mode is not allowed in the back scattering geometry of a c-plate crystal. Owing to the local symmetry breaking by PNRs, the TA mode appears slightly in a Brillouin spectrum.…”

“…This elastic anomaly clearly shows thermal hysteresis, and below T C , noticeable aging appears and its relaxation time becomes longer as the Sr content x increases. [12][13][14] The temperature dependence of LA velocity was fitted by the following power law…”

“…Quenched fluctuations of RFs are known to stabilize polar nanoregions (PNRs) which contribute essentially to the precursor phenomena of a relaxor ferroelectric phase transition. [12][13][14] In the present study, the effect of very weak RFs on the elastic properties of SBN26 (x = 0.26) single crystals was investigated using Brillouin scattering spectroscopy. The observed results of SBN26 are finally compared to those of SBN80 (x = 0.80) with strong RFs.…”