Infrared, Raman, and Electron Spin Resonance Studies of Vitreous Alkaline Tungsten Phosphates and Related Glasses

Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P₂O₅–WO₃–A₂O (A = Li, Na). Structural approach of the highly modified glasses P₂O₅–A₂MoO₄–A₂O (M = Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO₆octahedra, MO₄tetrahedra, M₂O₇dimers, PO₄tetrahedra, and also P₂O₇or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A₂O increases. ESR experiments were conducted on both X-ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W⁵⁺ and Mo⁵⁺ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus–oxygen–hole–center and peroxy radicals. The M⁵⁺ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted for vitreous materials.     

Sulfonated poly(hexamethylene terephthalate) copolyesters: Enhanced thermal and mechanical properties

A series of poly(hexamethylene terephthalate‐co‐hexamethylene 5‐sodium sulfoisophthalate) copolyesters containing from 5 to 50 mol % of sulfonated units as well as the two parent homopolymers are prepared by melt polycondensation. The polyesters are obtained with high molecular weights, which decrease with the increased content of sulfonated units in the copolymer. Polyesters with 5 and 10 mol % of sulfonated units are semicrystalline whereas for contents equal or above 20 mol % they are unable to crystallize from the melt. Thermogravimetric analysis show that the thermal stability decreases with the content in sulfonated units. Isothermal crystallizations of semicrystalline copolyesters show that the insertion of the sulfonated units causes a reduction of crystallizability, most probably due to the occurrence of ionic aggregations. It is observed a synergistic effect on the mechanical properties for copolymers with contents of around 5 mol % where the elongation at break increases drastically. Moreover, the hydrolytic degradation of the copolymer is enhanced with the content in sulfonated units. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Magnetic and Electronic Properties of Point Defects in ZrO2

Using the Korringa–Kohn–Rostoker Coherent Potential Approximation (KKR-CPA) method in connection with the Generalized Gradient Approximation (GGA), we study the magnetic and electronic properties of different point defects in cubic ZrO₂. In particular, we discuss the zirconium interstitial (Zr_i), zirconium antisite (Zr_O), zirconium vacancy (V_Zr), oxygen interstitial (O_i), oxygen antisite (O_Zr), and oxygen vacancy (V_O) defects. It has been shown that oxygen vacancy and zirconium interstitial (V_O, Zr_i) are n-type, while the other point defects are p-type. The magnetic moments are observed only in the oxygen interstitial and antisite (O_i, O_Zr) cases. The corresponding ferromagnetic states are more stable than the spin–glass states. It has been found that the mechanism responsible of such stabilities is the double exchange. Based on Mean Field Approximation (MFA), the Curie temperature (T _C ) is estimated. Moreover, it has been found that the O_i and O_Zr defects provide half-metallic properties being the responsible for ferromagnetism.     

Contribution of side scan sonar to the management of Mediterranean littoral ecosystems

The bathymetric range of seagrass beds represents a valuable biological indicator of littoral water quality. In order to contribute to the management of this natural heritage, an attempt was made to determine the status of Posidonia oceanica seagrass beds along the Mediterranean Corsican coast. The manual interpretation of images obtained using side scan sonar was used to accurately determine the lower depth limit of P. oceanica (-32m) and this work confirms the overall good quality of the littoral waters in this region of the Mediterranean. Particular structures which are directly linked to various human activities were identified manually, however, as were differences in sonogram texture. An attempt was thus made to automate processing of the sonograms in order to accurately identify and quantify these different formations.     

Electronic and magnetic properties of semimagnetic semiconductors Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te

The electronic and the magnetic of semimagnetic semiconductors Hg_1−x Mn _x Te are studied. The magnetic phase diagrams have been determined by the replica method in the framework of the XY model using variational principle. A spin glass state has been obtained for x<x _c (x _c≈0.6). This phase is attributed to the randomness and the frustration of the antiferromagnetic interactions between the Mn magnetic ions arising from the topology of semimagnetic semiconductors Hg_1−x Mn _x Te. The sp³ semiempirical nearest-neighbor tight-binding formalism is used to compute the band structures of the above two systems in the hole range of concentration 0≤x≤1. The variation of the gap energy E _g with x is plotted.     

Electronic and Magnetic Properties of MnSb Compounds

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnSb compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The ferromagnetic energy of MnSb systems is obtained. Magnetic moment considered to lie along the (001) axes are computed. The exchange interactions between the magnetic atoms Mn–Mn in MnSb are given using the mean field theory. Obtained data from ab initio calculations are used as input for the high-temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The HTSEs of the magnetic susceptibility of the magnetic moments in MnSb (m _Mn) is given up to the tenth order series in (x = J ₁(Mn–Mn)/ k _B T). The critical temperature T _C is deduced by HTSEs of the magnetic susceptibility series combined with the Padé approximation method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.