Role of polar nanoregions with weak random fields in Pb-based perovskite ferroelectrics

Abstract

In relaxor ferroelectrics, the role of randomly orientated polar nanoregions (PNRs) with weak random fields (RFs) is one of the most puzzling issues of materials science. The relaxation time of polarization fluctuations of PNRs, which manifests themselves as a central peak (CP) in inelastic light scattering, is the important physical quantity to understand the dynamics of PNRs. Here, the angular and temperature dependences of depolarized and polarized CPs in 0.44Pb(Mg1/3Nb2/3)O3-0.56PbTiO3 single crystals with weak RFs have been studied by Raman and Brillouin scattering, respectively. The CPs observed in Raman scattering show the very clear angular dependence which is consistent with the local tetragonal symmetry. It is different from the well-known local rhombohedral symmetry with strong RFs for Pb(Mg1/3Nb2/3)O3. In Brillouin scattering, depolarized and polarized CPs show two relaxation processes corresponding to transverse and longitudinal fluctuations of PNRs. The remarkable slowing down towards the Curie temperature was observed for transverse fluctuations in local tetragonal symmetry.

Local Structural Heterogeneity and Electromechanical Responses of Ferroelectrics: Learning from Relaxor Ferroelectrics

“…This type of relaxors includes PMN, PZN, PbSc 1/2 Nb 1/2 O 3 (PSN), PbSc 1/2 Ta 1/2 O 3 (PST), Na 1/2 Bi 1/2 TiO 3 (NBT), etc., which generally contain two heterovalance cations on the A‐site or B‐site of the perovskite structure. In these relaxors, the A‐site or B‐site cations are not totally ordered, instead, both nanoscale ordering and disordered regions may be present . For some systems, the volume fraction of the ordered regions can be tuned by thermal annealing.…”

Domain Engineering Enabled Giant Linear Electro‐Optic Effect and High Transparency in Ferroelectric KTa1−xNbxO3 Single Crystals

“…PNRs are formed due to the reorientation of off‐center Nb ions described by these three characteristic temperatures, from lowest to highest: the Curie temperature, ; intermediate temperature, ; and Burns temperature, , respectively. [ 32–35 ] As we increase the temperature from to ( T > ), these microscopically small static FE regions within its macroscopic PE state start to shrink in size, correlation, and lifetime. Ta ions move toward their high symmetry site and Nb ions get de‐restricted of specific reorientation directions upon approaching .…”

Influence of calcium doping on microstructure, dielectric and electric properties of BaBi2Nb2O9 ceramics

“…The increase in homogeneity of grain sizes corresponds to the increase in intergranular porosity and resulted in the decrease in relative density. The density of the unmodified ceramics, obtained by the Archimedes displacement method with distilled water, was 7.07 g/cm 3 , whereas the density of the ceramics modified with 5 at.% of calcium was 6.94 g/cm 3 . The changes of the morphology and grain size may not solely be an effect of doping, but also the difference in the sintering temperature (the pure BBN ceramics were sintered at 1100°C, whereas the calcium modified ones at 1150°C).…”

“…Over the past few decades a number of theoretical models have been developed to try to describe their properties. Their basic assumption is existence of polar nanoregions (PNRs), which provide unique physical properties [1][2][3]. Although the presence of PNRs in ferroelectric relaxors is noticed without a doubt, the mechanism and reasons for their formation have been the subject of discussion for several decades.…”