X-ray absorption spectroscopic study of the mixed valence system CePd3

Mixed valency in CePd3 has been examined by a study of the LIII (Ce) absorption edge in this compound as well as other model compounds. In CePd3, peaks characteristic of 3+ and 4+ states of Ce are found to be separated by 2 eV.

High Lithium Storage in Mixed Crystallographic Phase Nanotubes of Titania and Carbon-Titania

Morphology and electrochemical performance of mixed crystallographic phase titania nanotubes for prospective application as anode in rechargeable lithium ion batteries are discussed. Hydrothermally grown nanotubes of titania (TiO2) and carbon-titania (C-TiO2) comprise a mixture of both anatase and TiO2 (B) crystallographic phases. The first cycle capacity (at Current rate = 10 mAg(-1)) for bare TiO2 nanotubes was 355 mAhg(-1) (approximately 1.06 Li), which is higher than both the theoretical capacity (335 mAhg(-1)) and the reported values for pure anatase and TiO2 (B) nanotubes. Higher capacity is attributed to it combination of the presence of mixed crystallographic phases of titania and trivial size effects. The surface area of bare TiO2 nanotubes was very high at 340 m(2) g(-1). C-TiO2 nanotubes showed a slightly lower first-cycle specific capacity of 307 mAhg(-1), but the irreversible capacity loss in the first cycle decreased by half compared to bare TiO2 nanotubes. The C-TiO2 nanotubes also showed a better rate capability, that is, higher capacities compared to bare TiO2 nanotubes in the Current range 0.1-2 Ag-1. Enhanced rate capability in the case of C-TiO2 is attributed to the efficient percolation of electrons as well its to the decrease in the anatase phase.

A new mixed-matrix membrane for DMFCs

A new mixed-matrix membrane based on stabilized phosphotungstic acid (PTA) incorporated to chitosan (CS)-hydroxy ethyl cellulose (HEC) for application in direct methanol fuel cells (DMFCs) is reported. Membranes are characterised using Fourier Transform Spectroscopy (FTIR), Thermo-Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and their mechanical properties are evaluated. The PTA content in the CS-HEC blend and its influence on proton conductivity, water/methanol sorption, and methanol cross-over in the DMFC is studied. The DMFC with 3 wt. % stabilized PTA-CS-HEC mixed-matrix membrane delivers peak power-density of 58 mW/cm(2) at a load current-density of 210 mA/cm(2) with a lower methanol cross-over than that observed for a DMFC operating with a Nafion membrane electrolyte.

Unsteady MHD mixed convection flow over an impulsively stretched permeable vertical surface in a quiescent fluid

The unsteady mixed convection flow of an incompressible laminar electrically conducting fluid over an impulsively stretched permeable vertical surface in an unbounded quiescent fluid in the presence of a transverse magnetic field has been investigated. At the same time, the surface temperature is suddenly increased from the surrounding fluid temperature or a constant heat flux is suddenly imposed on the surface. The problem is formulated in such a way that for small time it is governed by Rayleigh type of equation and for large time by Crane type of equation. The non-linear coupled parabolic partial differential equations governing the unsteady mixed convection flow under boundary layer approximations have been solved analytically by using the homotopy analysis method as well as numerically by an implicit finite difference scheme. The local skin friction coefficient and the local Nusselt number are found to decrease rapidly with time in a small time interval and they tend to steady-state values for t* >= 5. They also increase with the buoyancy force and suction, but decrease with injection rate. The local skin friction coefficient increases with the magnetic field, but the local Nusselt number decreases. There is a smooth transition from the unsteady state to the steady state. (C) 2010 Elsevier Ltd. All rights reserved.

Mixed saturated-unsaturated alkyl-chain assemblies: Solid solutions of zinc stearate and zinc oleate

The linear saturated stearic acid and the bent mono-unsaturated oleic acid do not mix and form solid solutions. However, the zinc salts of these acids can. From X-ray diffraction and DSC measurements we show that the layered zinc stearate and zinc oleate salts form a homogeneous solid solution at all composition ratios. The solid solutions exhibit a single melting endotherm, with the melting temperature varying linearly with composition but with the enthalpy change showing a minimum. By monitoring features in the infrared spectra that are characteristic of the global conformation of the hydrocarbon chain, and hence can distinguish between stearate and oleate chains, it is shown that solid solution formation is realized by the introduction of gauche defects in a fraction of the stearate chains that are then no longer linear. This fraction increases with oleate concentration. It has also been possible from the spectroscopic measurements to establish a quantitative relation between molecular conformational order and the thermodynamic enthalpy of melting of the solid solutions.

Family of Mixed-Valence Oxovanadium(IV/V) Dinuclear Entities Incorporating N4O3-Coordinating Heptadentate Ligands: Synthesis, Structure, and EPR Spectra

Dinuclear ((VVV)-V-IV) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N-2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L1), 2,6-bis[{{(5-methyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L2) 2,6-bis[ {{(5-tert-butyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenoI (H3L3), 2,6-bis[{{(5-chloro-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L4) , 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L6). In [V2O3L1], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V...V=O torsion angle is 24.6(2)degrees. The V-O-oxo-V and V-O-phenoxo-V angles are 117.5(4) and 93.4(3)degrees, respectively. The V...V bond distance is 3.173(5) Angstrom. X-ray crystallography, IR, UV-vis, and H-1 and V-51 NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type 111). The thermal ellipsoids of O2, O4, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3d(xy)(1)). Valence localization at 77 K is also consistent with the V-51 hyperfine structure of the axial EPR spectra (3d(xy)(1) ground state) of the complexes in frozen (77 K) dichloromethane solution: S = 1/2, g(parallel to) similar to 1.94, g(perpendicular to) similar to 1.98, A(parallel to) similar to 166 x 10(-4) cm(-1), and A(perpendicular to) similar to 68 x 10(-4) cm(-1). In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (g(iso) similar to 1.974 and A(iso) similar to 50 x 10(-4) cm(-1)) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L1].CH2Cl2 complex are as follows: chemical formula, C32H43O6N4C12V2; crystal system, monoclinic; space group, C2/c; a = 18.461(4), b = 17.230(3), c = 13.700(3) Angstrom; beta = 117.88(3)degrees; Z = 8.

A novel sheet 4f-3d mixed-metal pyridine dicarboxylate: synthesis, structure, photophysical properties and its transformation to a perovskite oxide

The synthesis, characterization and photophysical properties of a 4f-3d mixed metal compound, Gd(H2O)(3)Co[C5N1H3-(COO)(2)](3), are described; the structure is unique, consisting of sheets with large pores ( ca. 7 angstrom diameter) in the sheets and transforms to a perovskite oxide at moderate temperatures.

PVA-SSA-HPA Mixed-Matrix-Membrane Electrolytes for DMFCs

Stabilized forms of heteropolyacids (HPAs), namely phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA), are incorporated into poly (vinyl alcohol) (PVA) cross-linked with sulfosuccinic acid (SSA) to form mixed-matrix membranes for application in direct methanol fuel cells (DMFCs). Bridging SSA between PVA molecules not only strengthens the network but also facilitates proton conduction in HPAs. The mixed-matrix membranes are characterized for their mechanical stability, sorption capability, ion-exchange capacity, and wetting in conjunction with their proton conductivity, methanol permeability, and DMFC performance. Methanol-release kinetics is studied ex situ by volume-localized NMR spectroscopy (employing point-resolved spectroscopy'') with the results clearly demonstrating that the incorporation of certain inorganic fillers in PVA-SSA viz., STA and PTA, retards the methanol-release kinetics under osmotic drag compared to Nafion, although PVA-SSA itself exhibits a still lower methanol permeability. The methanol crossover rate for PVA-SSA-HPA-bridged-mixed-matrix membranes decreases dramatically with increasing current density rendering higher DMFC performance in relation to a DMFC using a pristine PVA-SSA membrane. A peak power density of 150 mW/cm(2) at a load current density of 500 mA/cm(2) is achieved for the DMFC using a PVA-SSA-STA-bridged-mixed-matrix-membrane electrolyte. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3465653] All rights reserved.

Solid-state chemistry of high-temperature oxide superconductors:The experimental situation

High-temperature superconductivity in oxides of the type(La, Ln)2?xBax(Sr)xCuO4, Y(Ln)Ba2Cu3O7??, La3?xBa3+xCu6O14, and related systems is discussed with emphasis on aspects related to experimental solid-state chemistry. All of these oxides possess perovskite-related structures. Oxygen-excess and La-deficient La2CuO4 also exhibit superconductivity in the 20�40 K just as La2?xBax(Srx)CuO4; these oxides are orthorhombic in the superconductivity phase. The crucial role of oxygen stoichiometry in the superconductivity ofYBa2Cu3O7?? (Tc = 95 ± 5K) is examined; this oxide remains orthorhombic up to ? ? 0.6 and becomes tetragonal and nonsuperconducting beyond this value of ?. Oxygen stoichiometry in this and related oxides has to be understood in terms of structure and disorder. The structure of La3?xBa3+xCu6O14 is related to that of YBa2Cu3O7, the orthorhombic structure manifesting itself when the population of O1 oxygens (along the Cusingle bondOsingle bondCu chains) is preponderant compared to that of O5 oxygens (along thea-axis); nearly equal populations of O1 and O5 sites give rise to the tetragonal structure. A transition from a high-Tc (95 K) superconductivity regime to a low-Tc (not, vert, similar60 K) regime occurs in YBa2Cu3O7?? accompanying a change in ?. There is no evidence for Cu3+ in these nominally mixed valent copper oxides. Instead, holes are present on oxygens giving rise to O? or O2?2 species, the concentration of these species increasing with the lowering of temperature. Certain interesting aspects of the superconducting oxides such as domain or twin boundaries, Raman spectra, microwave absorption, and anomalous high-temperature resistivity drops are presented along with the important material parameters. Preparative aspects of the superconducting oxides are briefly discussed. Phase transitions seem to occur atTc as well as at not, vert, similar240 K in YBa2Cu3O7.

Fe-57 Mössbauer and Mo K-EXAFS Investigations of MoxFe3-xO4, an Interesting Mixed-Valent Oxide System

Ferrites of the formula MoxFe3-xO4, prepared by a soft-chemistry route, show mixed valence states of both iron and molybdenum cations. Mössbauer studies show that Fe2+ and Fe3+ ions are present on both the A and B sites, giving Fe an average oxidation state between 2+ and 3+. Molybdenum is present in the 3+ and the 4+ states on the B sites. The presence of Mo in the 3+ state has been established by determining the Mo3+-O distance (2.2 Å), for the first time, by Mo K-EXAFS. The mixed valence of Fe on both the A and B sites and of Mo on the B sites is responsible for the fast electron transfer between the cations. All the Mössbauer parameters including the line width show a marked change at a composition (x ? 0.3) above which the concentration of Fe2+A increases rapidly.

Reduction behaviour of Fe3+/Al2O3 obtained from the mixed oxalate precursor and the formation of the Fe0-Al2O3 metal-ceramic composite

Reduction behaviour of Fe3+/Al2O3 obtained by the decomposition of the oxalate precursor has been investigated by employing X-ray diffraction (XRD), Mössbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Calcination of Fe3+/Al2O3 at or below 1070 K yields mainly a poorly ordered, fine particulate form of ?-Al2�xFexO3. Calcination at or above 1220 K yields ?-Al2�xFexO3. Reduction of Fe3+/Al2O3 samples calcined at or below 1070 K gives the FeAl2O4 spinel on reduction at 870 K; samples calcined at or above 1220 K give Al2-xFexO3 with a very small proportion of metallic iron. Fe3+/Al2O3 samples calcined at 1220 K or above yield metallic iron and a very small proportion of the spinel on reduction below 1270 K. In the samples reduced at or above 1270 K, the main product is metallic iron in both ferromagnetic and superparamagnetic forms. The oxalate precursor route yields more metallic iron than the sol�gel route.

Thermodynamic Study of Mixed Anionic Solid Solutions Using Gradient Solid Electrolytes System K2CO3 - K2SO4

The thermodynamic properties of K2CO3 -KSO, solid solutions with hexagonal structure have been measured using a solid-state cell, incorporating a composite solid electrolyte with step-changes in composition. The cell with the configuration Pt, CO2' + O2' || K2CO3 | K2(CO3)x(SO4)1-x || CO2'' + O2'' + Pt X =1 X=X was investigated in the temperature range of 925 to 1165 K. The composite gradient solid electrolyte consisted of pure K2CO3 at one extremity and the solid solution under study at the other. The Nernstian response of the cell to changes in partial pressures of CO2 and O2 at the electrodes and temperature was demonstrated. The activity of K2CO3 in the solid solution was measured by three techniques. All three methods gave identical results, indicating unit transport number for K+ ions and negligible diffusion potential due to concentration gradients of carbonate and sulfate ions. The activity of K2CO3 exhibits positive deviation from Raoult's law. The excess Gibbs energy of mixing of the solid solution can be represented using a subregular solution model DELTAG(E) = X(1 - X)[5030X + 4715(1 - X)] J mol-1 By combining this information with the phase diagram, mixing properties of the liquid phase were obtained.

Correlations, quantum entanglement and interference in nanoscopic systems

Several of the most interesting quantum effects can or could be observed in nanoscopic systems. For example, the effect of strong correlations between electrons and of quantum interference can be measured in transport experiments through quantum dots, wires, individual molecules and rings formed by large molecules or arrays of quantum dots. In addition, quantum coherence and entanglement can be clearly observed in quantum corrals. In this paper we present calculations of transport properties through Aharonov-Bohm strongly correlated rings where the characteristic phenomenon of charge-spin separation is clearly observed. Additionally quantum interference effects show up in transport through pi-conjugated annulene molecules producing important effects on the conductance for different source-drain configurations, leading to the possibility of an interesting switching effect. Finally, elliptic quantum corrals offer an ideal system to study quantum entanglement due to their focalizing properties. Because of an enhanced interaction between impurities localized at the foci, these systems also show interesting quantum dynamical behaviour and offer a challenging scenario for quantum information experiments.

Entanglement and nonclassicality for multimode radiation-field states

Nonclassicality in the sense of quantum optics is a prerequisite for entanglement in multimode radiation states. In this work we bring out the possibilities of passing from the former to the latter, via action of classicality preserving systems like beam splitters, in a transparent manner. For single-mode states, a complete description of nonclassicality is available via the classical theory of moments, as a set of necessary and sufficient conditions on the photon number distribution. We show that when the mode is coupled to an ancilla in any coherent state, and the system is then acted upon by a beam splitter, these conditions turn exactly into signatures of negativity under partial transpose (NPT) entanglement of the output state. Since the classical moment problem does not generalize to two or more modes, we turn in these cases to other familiar sufficient but not necessary conditions for nonclassicality, namely the Mandel parameter criterion and its extensions. We generalize the Mandel matrix from one-mode states to the two-mode situation, leading to a natural classification of states with varying levels of nonclassicality. For two-mode states we present a single test that can, if successful, simultaneously show nonclassicality as well as NPT entanglement. We also develop a test for NPT entanglement after beam-splitter action on a nonclassical state, tracing carefully the way in which it goes beyond the Mandel nonclassicality test. The result of three-mode beam-splitter action after coupling to an ancilla in the ground state is treated in the same spirit. The concept of genuine tripartite entanglement, and scalar measures of nonclassicality at the Mandel level for two-mode systems, are discussed. Numerous examples illustrating all these concepts are presented.