Phase transition of the uniaxial disordered ferroelectric Sr_0.61Ba_0.39Nb₂O₆

Abstract

Abstract. We report a neutron scattering study of a ferroelectric phase transition in Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN-61).The ferroelectric polarization is along the crystallographic c-axis but the transverse acoustic branch propagating along the <1, 1, 0> direction does not show any anomaly associated with the this transition. We find no evidence for a soft transverse optic phonon. We do, however, observe elastic diffuse scattering. The intensity of this scattering increases as the sample is cooled from a temperature well above the phase transition. The susceptibility associated with this diffuse scattering follows well the anomaly of the dielectric permittivity of SBN-61. Below T c the shape of this scattering is consistent with the scattering expected from ferroelectric domain walls. Our results suggest that despite apparent chemical disorder SBN-61 behaves as a classic order-disorder uniaxial ferroelectric with critical fluctuations in the range < 10 −11 s.

Dynamics of Nanoscale Polarization Fluctuations in a Uniaxial Relaxor

“…At the same time, the Lorentzian profile of the OPF diffuse scattering component within the a à b à reciprocal plane has been thoroughly studied in the past and its 5-10 unit cell transverse correlation length is well established [51][52][53]. Therefore, the present results allow us to combine the information about temporal and spatial correlations associated with Vogel-Fulcher-type dielectric relaxations of SBN61.…”

“…It was found that the intensity profile of the narrower component, monotonically increasing with decreasing temperature, can be well described by a simple model for scattering by domain walls and that its presence can be effectively suppressed by a bias electric field of a few kV=cm [51,53,54]. On the other hand, the intensity of the broader component has a temperature dependence similar to the dielectric permittivity with a maximum near T max and the electric field has a much smaller influence here.…”

“…Detailed neutron scattering studies revealed that this diffuse scattering actually consists of two contributions with a distinct temperature dependence and with a distinct shape in the momentum space [51][52][53]. It was found that the intensity profile of the narrower component, monotonically increasing with decreasing temperature, can be well described by a simple model for scattering by domain walls and that its presence can be effectively suppressed by a bias electric field of a few kV=cm [51,53,54].…”

“…On the other hand, the intensity of the broader component has a temperature dependence similar to the dielectric permittivity with a maximum near T max and the electric field has a much smaller influence here. Accordingly, the two components have been assigned to scattering due to static domain walls (DW) and due to the order parameter fluctuations (OPF), respectively [51][52][53]. Both the DW and the OPF components have been reported as elastic within the resolution limits of the corresponding neutron three-axis spectrometer experiments, which only means that such scattering is due to lattice modulations that are either static or fluctuating at frequencies lower than about 100 GHz, without a possibility of making any statement about their behavior in the GHz=MHz range of the dielectric spectroscopy frequencies.…”

Phase transition of chemically doped uniaxial relaxor ferroelectric

“…There is a strong change in polarization aging under light illumination in SBN-61:Ce [14]. Thus, the macroscopic properties of doped SBN-61 crystals have much in common with relaxors.The phase transition of pure SBN-61 has been recently studied by neutron scattering [15][16][17]. On approaching from above the transition temperature, T C , a slow dynamic diffuse scattering (DS) emerges in the neutron spectra [16,17].…”