The phase diagram of the betaine arsenate-phosphate mixed crystal system by measurement of the dielectric hysteresis and current curves

The ferroelectric (FE) betaine arsenate (BA) and the antiferroelectric (AF) betaine phosphate (BP) are structurally very closely related and mixed crystals of BAxBP1-x can be grown over the whole concentration range. The concentration (x) – temperature (T) – pressure (P) phase diagram of the system is characterized by a transition from an AF to a FE phase along with the appearance of some mixed regions on changing concentration. Depending on concentration, one or two relaxation processes appear in the low temperature region of the phase diagram. Measurement of the hysteresis loops and the current curves have been carried out along the (x-T-P)-phase diagram of this system. Multiple loops have been observed in various regions of the phase diagram. The correlation of the different contributions of the polarization and the temperature behavior of their critical fields with the main features of the temperature and frequency dependent dielectric constant enables clarification of the rich phase diagram obtained in this mixed compounds in terms of the ferro- and/or antiferroelectric interactions

Raman and infrared study of the quasi-one-dimensional betaine arsenate-phosphate mixed-crystal system

Ferroelectric (FE) betaine arsenate (BA) and antiferroelectric (AF) betaine phosphate (BP) are structurally very closely related and mixed crystals BA(x)BP(1-x) can be grown over the full concentration range. This system exhibits interesting pressure-temperature-concentration phase diagrams in which the transition in concentration from an AF to a FE phase can be observed with a concentration-dependent appearance of some mixed regions. At low temperatures different relaxation processes have been observed that might be related to the transition from a domain state to an orientational glass depending on concentration. In some regions of the phase diagram different phases coexist. The origin of the different transitions and relaxation processes is still unclear and recent x-ray-diffraction studies reveal that the peculiar behavior of the mixed crystals cannot be explained from the structural point of view. We have performed Raman and infrared investigation of samples across the whole (x, T) phase diagram, at various hydrostatic pressures, in order to shed light on the structural origin of the different processes. It is concluded that the FE or AF character of the ordered phase is related to the degrees of freedom of the AsO4 and PO4 tetrahedra. In the same way these units determine the type and the modes triggering the phase transitions for each concentration. The latter seems to occur together with a participation of the betaine molecule, especially of the methyl and buthyl groups.info:eu-repo/semantics/publishedVersio

Comment on "On the TST_S-Anomaly in Betaine Calcium Chloride Dihydrate"

Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed the $T_S$-anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type approach. We comment on the shortcomings of this approach and discuss the $T_S$-anomaly in the framework of a microscopical pseudo spin model based on a realistic description of BCCD in terms of symmetry-adapted local modes.Comment: 2 pages, RevTex, submitted to J. Phys. Soc. Jp

Ferroelectric/antiferroelectric phase coexistence in the intermediate concentration regions of the BA(x)BP(1-x) phase diagram

Temperature and frequency dependent hysteresis loop measurements have been carried out along the phase diagram of ferroelectric (FE) betaine at-senate (BA) and antiferroelectric (AF) betaine phosphate (BP) mixed crystal system (BA(x)BP(1-x)). Coexistence regions characterized by competing ferro- and/or antiferroelectric interactions are detected by multiple hysteresis loops.(undefined

Far-infrared spectroscopy investigation and lattice dynamics simulations in CsCdBr3 and CsCdBr3: R3+ crystals

Polarized infrared reflectivity spectra of CsCdBr3 crystal were measured at temperatures 20 and 300 K in the wave number range of 10-650 cm-1. Frequencies and damping of the optically active lattice modes at the Brillouin zone center were determined. The lattice dynamics of CsCdBr3 crystal is studied in the framework of the rigid ion model, the phonon density of states, and the spectral representations of correlation functions of relative displacements of a Cd2+ ion and the nearest neighbor Br- ions in the perfect lattice are presented. The local dynamics of the lattice containing impurity rare-earth ions that form symmetrical pair centers substituted for three adjacent Cd2+ ions is analyzed with the formalism of lattice Green's functions. It is argued that resonance and localized vibrations whose frequencies lie near the boundary of the continuous phonon spectrum of a perfect lattice are induced in CsCdBr3: R3+ crystals. The corresponding vibronic satellites have been found in the optical spectra of symmetrical dimers in CsCdBr3: Yb3+, CsCdBr3: Tm3+, and CsCdBr3: Pr3+ single crystals

Chemical data assimilation estimates of continental U.S. ozone and nitrogen budgets during the Intercontinental Chemical Transport Experiment-North America

Global ozone analyses, based on assimilation of stratospheric profile and ozone column measurements, and NOy predictions from the Real-time Air Quality Modeling System (RAQMS) are used to estimate the ozone and NOy budget over the continental United States during the July-August 2004 Intercontinental Chemical Transport Experiment-North America (INTEX-A). Comparison with aircraft, satellite, surface, and ozonesonde measurements collected during INTEX-A show that RAQMS captures the main features of the global and continental U.S. distribution of tropospheric ozone, carbon monoxide, and NOy with reasonable fidelity. Assimilation of stratospheric profile and column ozone measurements is shown to have a positive impact on the RAQMS upper tropospheric/lower stratosphere ozone analyses, particularly during the period when SAGE III limb scattering measurements were available. Eulerian ozone and NOy budgets during INTEX-A show that the majority of the continental U.S. export occurs in the upper troposphere/lower stratosphere poleward of the tropopause break, a consequence of convergence of tropospheric and stratospheric air in this region. Continental U.S. photochemically produced ozone was found to be a minor component of the total ozone export, which was dominated by stratospheric ozone during INTEX-A. The unusually low photochemical ozone export is attributed to anomalously cold surface temperatures during the latter half of the INTEX-A mission, which resulted in net ozone loss during the first 2 weeks of August. Eulerian NOy budgets are shown to be very consistent with previously published estimates. The NOy export efficiency was estimated to be 24%, with NOx + PAN accounting for 54% of the total NOy export during INTEX-A. Copyright 2007 by the American Geophysical Union

Surface critical exponents at a uniaxial Lifshitz point

Using Monte Carlo techniques, the surface critical behaviour of three-dimensional semi-infinite ANNNI models with different surface orientations with respect to the axis of competing interactions is investigated. Special attention is thereby paid to the surface criticality at the bulk uniaxial Lifshitz point encountered in this model. The presented Monte Carlo results show that the mean-field description of semi-infinite ANNNI models is qualitatively correct. Lifshitz point surface critical exponents at the ordinary transition are found to depend on the surface orientation. At the special transition point, however, no clear dependency of the critical exponents on the surface orientation is revealed. The values of the surface critical exponents presented in this study are the first estimates available beyond mean-field theory.Comment: 10 pages, 7 figures include