Non-relaxor behaviour of low-frequency vibration spectra of relaxor ferroelectric PbCo1/3Nb2/3O3: evidences from Brillouin and Raman scattering measurements.

This paper presents the results of studies of a low-frequency vibration spectrum of PbCo1/3Nb2/3O3 (PCN) relaxor ferroelectric crystal using the Brillouin and Raman light scattering in the temperature range from 80 to 750 K. The analysis of the temperature behaviour of the longitudinal acoustic phonon in Brillouin scattering spectra showed no anomalies in the vicinity of 'diffuse phase transition' (T m = 250 K) in PCN. Polarized Raman light scattering spectra were obtained in PCN over the entire temperature range studied. Analysis of low-frequency optical mode behaviour in PCN during temperature change also revealed no correlations with dielectric permeability anomaly in the vicinity of T m: softening of optical phonon at 43 cm-1 frequency in VV polarization is observed at 170 K. In the same temperature range, there are anomalies (a 'narrow' and weak component) in quasi-elastic light scattering (QELS) obtained in temperature behaviour with VH polarization in Raman spectra in PCN. A 'wide' and intense QELS component, obtained in Raman spectra with VV polarization, shows anomalies in the vicinity of T m. We associate the anomalies of optical phonons and QELS with structure distortions in the formation of phase stratification and the dynamics of polar nano-regions.

Phase transition of chemically doped uniaxial relaxor ferroelectric.

We report a neutron scattering study of the ferroelectric phase transition in Sr0.585Ce0.025Ba0.39Nb2O6 (SBN-61:Ce). We find no evidence for a soft transverse optic phonon. We do, however, observe anisotropic diffuse scattering. This scattering has inelastic and elastic contributions. In the paraelectric phase the susceptibility associated with the elastic diffuse scattering from SBN-61:Ce increases on approaching the transition temperature. In the ferroelectric phase the lineshape of the elastic scattering is consistent with the form expected for the ferroelectric domain walls. In contrast to the macroscopic observations, the scattering properties of Ce-doped crystal do not exhibit important changes with respect to those of pure Sr0.61Ba0.39Nb2O6.

Phase transition of the uniaxial disordered ferroelectric Sr(0.61)Ba(0.39)Nb(2)O(6).

We report a neutron scattering study of a ferroelectric phase transition in Sr0.61Ba0.39Nb2O6 (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 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 the anomaly of the dielectric permittivity of SBN-61 well. Below Tc 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.

The structure and low-energy phonons of the nonferroelectric mixed perovskite: BaMg1/3Ta2/3O3.

The structure of BaMg(1/3)Ta(2/3)O(3) (BMT) has been studied using x-ray scattering. The phonons have been measured and the results are similar to those of other materials with a perovskite structure such as PbMg(1/3)Nb(2/3)O(3) (PMN). The acoustic and lowest energy optic branches were measured but it was not possible to measure the branches of higher energy, possibly this is because they largely consist of oxygen motions. High-resolution inelastic measurements also showed that the diffuse scattering was strictly elastic and not directly related to the phonon spectra. Diffuse scattering was observed in BMT near the (H ± 1/2, K ± 1/2, L ± 1/2) points in the Brillouin zone and these had a characteristic cube shape. This arises from ordering of the B-site ions in BMT. Additional experiments revealed the diffuse scattering in BMT similar in shape to Bragg reflections at wavevectors of the form (H ± 1/3, K ± 1/3, L ± 1/3). Such reflections were also observed by Lufaso (2004 Chem. Mater. 16 2148) from powders and suggest that this structure of BMT consists of four differently oriented domains of a trigonal structure and results from a different ordering of the B-site ions from that responsible for the scattering at the (H ± 1/2, K ± 1/2, L ± 1/2) points. The results lead us to suggest that for BMT single crystals the bulk has the properties of a cubic perovskite, whereas the surface may have quite different structure from that of the bulk. This difference resembles the behaviour of cubic relaxors like PMN and PMN doped by PbTiO(3), where significant surface effects have been reported.

Fractal properties of lysozyme: a neutron scattering study.

The spatial structure and dynamics of hen egg white lysozyme have been investigated by small-angle and inelastic neutron scattering. Analysis of the results was carried using the fractal approach, which allowed determination of the fractal and fracton dimensions of lysozyme, i.e., consideration of the protein structure and dynamics by using a unified approach. Small-angle neutron scattering studies of thermal denaturation of lysozyme have revealed changes in the fractal dimension in the vicinity of the thermal denaturation temperature that reflect changes in the spatial organization of protein.

Manipulating the magnetic structure with electric fields in multiferroic ErMn2O5.

Based on measurements of soft x-ray magnetic diffraction under in situ applied electric field, we report on significant manipulation and exciting of commensurate magnetic order in multiferroic ErMn2O5. The induced magnetic scattering intensity arises at the commensurate magnetic Bragg position whereas the initial magnetic signal almost persists. We demonstrate the possibility to imprint a magnetic response function in ErMn2O5 by applying an electric field.

Evidence for a quasi-two-dimensional proton glass state in Cs5H3(SO4)(4); xH(2)O Crystals.

We describe damping of hypersonic and ultrasonic longitudinal acoustic (LA) phonons in crystals of Cs 5H (3)(SO (4))(4);xH 2O (PCHS) between 100 and 360 K. The damping of LA phonons exhibits strong dispersion caused by relaxation processes in the region of transformation into the glasslike phase (T(g) approximately 260 K). Near T(g) the damping of ultrasonic phonons propagating in the basal plane reflects the cooperative freezing of acid protons. The damping of LA phonons propagating perpendicular to the basal plane can be fit by the Debye model and is due to the interaction between protons and LA phonons. This suggests that the proton glass state that is realized at T