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Using atomic force microscopy and piezoresponse force microscopy (PFM), as well as complementary dielectric measurements, the ferroelectric domain structure of single crystals of pure and ruthenium (Ru)-doped 0.9Pb(Zn1/3Nb2/3)O3 (PZN)-0.1PbTiO3 (PT), and Ru/(Zn+Nb+Ti)∼0.002 was analyzed. The coexistence of tetragonal and nontetragonal ferroelectric domains in PZN-PT near the morphotropic phase boundary (MPB) was directly observed via PFM imaging. The incorporation of Ru in the perovskite structure substantially decreases the ferroelectric domain size, thus reducing the polar fraction distributed in the pseudocubic matrix. The polarization and strain hysteresis loops show that Ru doping leads to significant ferroelectric hardening, which is attractive for high-power applications. The local structure and valent state of the incorporated Ru cations were additionally analyzed by electron paramagnetic resonance spectroscopy. Our results demonstrate that doping of tetragonal PZN-PT near MPB is a promising route to design advanced multifunctional single-crystal materials. [ABSTRACT FROM AUTHOR]

Raman spectroscopy was applied to study nano-scale structure and related phonon anomalies in relaxor-ferroelectric materials of type PbB′0.5B″0.5O3. By comparing the polarized spectra of single crystals, measured at temperature higher than the maximum of the dielectric permittivity, Tm, and by performing normal mode calculations the observed Raman peaks were assigned to definite atomic vibrations. Further, the temperature evolution of the phonon anomalies was investigated on the basis of calculated modes of representative structural units at various atomic positions. It is shown that within a few nm doubling of the unit cell should exist, independently of the degree of B-site ordering. The Raman activity of the silent F2u mode reveals the existence of dynamical off-centred structural fluctuations. The structural perturbation consists of a non-coplanarity of the Pb and O atoms in the planes perpendicular to the cubic body diagonal and non-centre-symmetrical deformations of the BO6 octahedra. On cooling, different structural changes are preferential: for B″=Nb the temperature decrease amplifies the deformation of the individual BO3–Pb species; for B″=Ta the temperature decrease favours the non-coplanarity of Pb and O atoms and enhances the correlation between the stereoactive electron lone pairs of Pb atoms. Besides, within nano-scale spatial regions, PbSc0.5Ta0.5O3 undergoes an additional phase transition near 180 K that involves a reduction of the rotational symmetry. The comparison between the temperature dependence of the inelastic light scattering in stoichiometric and Nb-doped PbSc0.5Ta0.5O3 shows that the presence of Nb even in small concentrations affects the Pb–O sublattice and changes the direction of the local structural transformations. [Copyright &y& Elsevier]

Local-scale atomic arrangements in three types of oxide crystalline materials with structural defects, self-bonded molecular sieves, ferroelastics and relaxor ferroelectricity, are investigated by Raman spectroscopy. The experimentally observed spectral data are analysed through normal mode calculations for structural species representative of the intermediate range order in the solid. In the case of molecular sieves, the important role of incipient structural species for producing crystalline silicalite-1 and zeolite beta spheres of mm size is shown. In the case of ferroelastics, further insights on structural perturbation across the domain walls in monoclinic Pb3(PO4)2 are provided. In the case of relaxors, the local structure and related dynamical effects in PbSc0.5Nb0.5O3 and PbSc0.5Nb0.5O3 is revealed. [ABSTRACT FROM AUTHOR]

Relaxor PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 single crystals are studied at room temperature using resonance Raman scattering. It is shown that the phonon modes associated with O localized BO6 vibrations in ferroic clusters strongly resonate in the vicinity of the maximum of the optical dielectric response function at 3.71 eV. Resonance Raman spectroscopy can be used to estimate the fraction and the average size of polar nanoclusters in the relaxor state. [ABSTRACT FROM AUTHOR]

Relaxor PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 single crystals are studied at room temperature using resonance Raman scattering. It is shown that the phonon modes associated with O localized BO6 vibrations in ferroic clusters strongly resonate in the vicinity of the maximum of the optical dielectric response function at 3.71 eV. Resonance Raman spectroscopy can be used to estimate the fraction and the average size of polar nanoclusters in the relaxor state. [ABSTRACT FROM AUTHOR]

Abstract: Nanosized zeolite Beta assemblies are prepared by a steam assisted conversion (SAC) method from micron-sized porous amorphous silica grains soaked in clear solutions containing the alumina source and organic template. The zeolite Beta assemblies are built of closely packed uniform nanocrystals (100nm) and retain the size and morphological features of the primary silica grains. The crystallinity and the phase purity depend strongly on the temperature and time of SAC treatment as well as on the initial aluminum content. For comparison, colloidal zeolite Beta samples with similar Si/Al ratio were prepared by a hydrothermal treatment (HT). The Raman and NMR spectroscopic data reveal that the method of preparation (SAC or HT) does not affect the local structure of Al-rich samples, while for high-silica samples the degree of disorder is higher in the ones obtained via the SAC approach. The adsorption/desorption isotherms of zeolite Beta assemblies and colloidal Beta powders indicate the presence of both micro- and mesoporosity. The catalytic behavior of the zeolite Beta assemblies and colloidal Beta powders in pentane hydroisomerization reaction is studied. [Copyright &y& Elsevier]