Universal Phase Diagram for High-Piezoelectric Perovskite Systems

Strong piezoelectricity in the perovskite-type PbZr(1-x)TixO3 (PZT) and Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) systems is generally associated with the existence of a morphotropic phase boundary (MPB) separating regions with rhombohedral and tetragonal symmetry. An x-ray study of PZN-9%PT has revealed the presence of a new orthorhombic phase at the MPB, and a near-vertical boundary between the rhombohedral and orthorhombic phases, similar to that found for PZT between the rhombohedral and monoclinic phases. We discuss the results in the light of a recent theoretical paper by Vanderbilt and Cohen, which attributes these low-symmetry phases to the high anharmonicity in these oxide systems.Comment: REVTeX file. 4 pages,=A0 4 figures embedde

Morphological Effects of Glycosaminoglycans on Calcium Oxalate Monohydrate Crystals

The effects of individual glycosaminoglycan (GAG) species on calcium oxalate monohydrate (COM) crystal growth were studied in vitro by the observation of crystal morphology grown in a supersaturated calcium oxalate solution in the presence of GAGs using optical and scanning electron microscopes. GAGs affected the morphology of COM crystals differently depending on the species. The growth rates of the crystals formed in the presence of chondroitin-6-sulfate (ChS-C) were higher in length and lower in width and thickness than those of control crystals. The incorporation of dermatan sulfate or heparin into the crystals formed in the presence of these GAGs was revealed by X-ray microanalysis, whereas ChS-C was not detected in the crystals grown with it. The experiment using dicarboxylates, as a simple model of GAG molecules, showed that a distance between the side groups was important for their morphological effects. These findings suggested that the different effects of GAGs on the crystal morphology resulted from the differences in their interaction modes with COM crystal faces, that is, the differences in their binding behavior, their inhibition modes of crystal growth, and other roles played after binding to the crystals

Spin Correlations in the Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2MnF4

We report a neutron scattering study of the instantaneous spin correlations in the two-dimensional spin S=5/2 square-lattice Heisenberg antiferromagnet Rb_2MnF_4. The measured correlation lengths are quantitatively described, with no adjustable parameters, by high-temperature series expansion results and by a theory based on the quantum self-consistent harmonic approximation. Conversely, we find that the data, which cover the range from about 1 to 50 lattice constants, are outside of the regime corresponding to renormalized classical behavior of the quantum non-linear sigma model. In addition, we observe a crossover from Heisenberg to Ising critical behavior near the Neel temperature; this crossover is well described by a mean-field model with no adjustable parameters.Comment: 8 pages, LaTeX, with 6 included EPS figures, submitted to EPJ

An Anomalous Phase in the Relaxor Ferroelectric Pb(Zn1/3_{1/3}Nb2/3_{2/3})O3_3

X-ray diffraction studies on a Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN) single crystal sample show the presence of two different structures. An outer-layer exists in the outer most $\sim$ 10 to 50~$\mu$m of the crystal, and undergoes a structural phase transition at the Curie temperature $T_C\approx410$ K. The inside phase is however, very different. The lattice inside the crystal maintains a cubic unit cell, while ferroelectric polarization develops below $T_C$. The lattice parameter of the cubic unit cell remains virtually a constant, i.e., much less variations compared to that of a typical relaxor ferroelectric, in a wide temperature range of 15 K to 750 K. On the other hand, broadening of Bragg peaks and change of Bragg profile line-shapes in both longitudinal and transverse directions at $T_C$ clearly indicate a structural phase transition occurring.Comment: to be submitted for PR

Anisotropy of the incommensurate fluctuations in Sr2RuO4: a study with polarized neutrons

The anisotropy of the magnetic incommensurate fluctuations in Sr2RuO4 has been studied by inelastic neutron scattering with polarized neutrons. We find a sizeable enhancement of the out of plane component by a factor of two for intermediate energy transfer which appears to decrease for higher energies. Our results qualitatively confirm calculations of the spin-orbit coupling, but the experimental anisotropy and its energy dependence are weaker than predicted.Comment: 4 pages, 4 figure

3)Soft Zone-Boundary Phonon Modes in CsPbCl_3

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Intercalation and Staging Behavior in Super-Oxygenated La2CuO4+δLa_2CuO_{4 + \delta}

A high temperature electrochemical oxidation process has been used to produce large single crystals of $La_2CuO_{4 + \delta}$ suitable for neutron scattering experiments. Below room temperature the oxygen-rich phases have structural superlattice scattering peaks which indicate new periodicities ranging from 2 to 6.6 layers perpendicular to the copper oxide planes. A model structure originally proposed for $La_2NiO_{4 + \delta}$ can account for the superlattice peaks as a result of anti-phase domain boundaries between different tilt directions of the CuO$_6$ octahedra. Within this model, the changes in CuO$_6$ tilt directions are induced by segregated layers of interstitial oxygen which order in a manner similar to intercalants in graphite. This structural model thus clarifies previous work and establishes $La_2CuO_{4 + \delta}$ as a unique lamellar superconducting system with annealed disorder.Comment: 23 pages, latex, 6 figures (not including Figures 2 & 7 and Table 1 which were not submitted but are available upon request to the Authors at: [email protected]