Chemical synthesis and magnetic properties of HCP and FCC nickel nanoparticles

In this study, we successfully synthesized single-phase hexagonal closed packed (HCP) and face-centered cubic (FCC) nickel nanoparticles via reduction of nickel nitrate hexahydrate and nickel acetate tetrahydrate, respectively, in polyethylene glycol-200. Structural information of the as-synthesized nickel nanoparticles are studied by X-ray diffraction (XRD) as a function of the molar concentration of the nickel precursor. XRD results reveal that low concentrations of nickel precursor (0.005?M and below) favor the HCP, while high concentrations favor the mixture of HCP and FCC crystal structures. Particle size of HCP structure is found in the range of ～15?nm via transmission electron microscope analysis. Vibratory sample magnetometer is employed to study its magnetic behavior and the results reveal that FCC crystalline phase shows ferromagnetic nature with high saturation magnetization (M _s?～?39.6?emu?gm^?1) as compared to metastable HCP crystalline structure (M _s?～?2?emu?gm^?1). The surfactants bonding on the surface of nickel nanoparticles are studied.     

High oxygen pressures and the stabilization of six-coordinated Ir(VI) in an oxygen lattice

Abstract

During these last twenty five years a great efforts have been made in the Laboratoire de Chimie du Solide du CNRS in order to develop high oxygen pressure for the stabilization of unusual oxidation state of transition elements.

The aims of such research works was to correlate the increase of the Mⁿ⁺-O bond covalency versus the increase of the oxidation state n+ to the physicochemical properties of resulting oxides [1].

Iridium was an interesting element due to its position (5d) in the Periodic Table. In 1980 Ir(V) (d⁴) was stabilized in La₂LiIrO₆ in the perovskite structure [2]. Such a study had underlined the strong value of the spin-orbit coupling associated to Ir(V) [3].

The stabilization of Ir(VI) is interesting from two points of view : (i) its isotropic electronic configuration (d³), (ii) such a high oxidation state could lead to the strongest M-O bond in an oxygen lattice.

Selecting, through a specific methodology, the most appropriate local structural and chemical factors and with the help of high oxygen pressure, Ir(V1) was stabilized in the perovskite Ba₂CaIrO₆. Structural, magnetic and Mössbauer studies have been carried out in order to characterize the physicochemical properties induced by this unusual oxidation state.     

Spectral Studies On Some 2-Quinolones

Spectral properties of some 2-Quinolones were investigate-ed. IR and ¹H NMR were applied to characterize the ligands. The hydrogen bond property is of important parameter for controlling the behaviour of the compounds. The N[sbnd]H, O[sbnd]H, C[dbnd]O, C[sbnd]H, and C[sbnd]N fundamental functional groups are characterized. The electronic transitions are assigned. The data are explained on the basis of molecular structure and substituents effects. The acid-base equilibria and the phenomena of tautomerism for these compounds are explained and discussed. The acid exponents (pK_OH, and pK_NH) are evaluated.     

Collective Modes and Elastic Constants of Liquid Al83Cu17 Binary Alloy

The collective dynamics （longitudinal and transverse phonon modes） are studied for aluminum-copper （Al-Cu） binary alloy in terms of the eigen-frequencies of the localized collective excitations. The model pseudopotential formalism is employed using a self-consistent phonon scheme by involving multiple scattering and phonon eigen- frequencies. These frequencies are expressed in terms of many-body correlation functions of atoms as well as of interatomic potential. The important ingredients in the present study are the pair-potential and pair-correlation functions. The most recent and sparingly used local field correlation functions are employed to investigate the influence of the screening effects on the vibrational dynamics of non-crystalline Al83Cu17 binary alloy. The results for the elastic constants like bulk modulus BT, rigidity modulus C, Poisson＇s ratio ξ, Young＇s modulus Y, Debye temperature 8D, propagation velocity of elastic waves and dispersion curves are reported based on the collective modes of this binary alloys. The present results are consistent and confirm the applicability of model potential and self-consistent phonon theory for such studies.     

Automatically tunable continuous-wave optical parametric oscillator for high-resolution spectroscopy and sensitive trace-gas detection

We present a high-power (2.75 W), broadly tunable (2.75–3.83 μm) continuous-wave optical parametric oscillator based on MgO-doped periodically poled lithium niobate. Automated tuning of the pump laser, etalon and crystal temperature results in a continuous wavelength coverage up to 450 cm^-1 per poling period at <5×10^-4 cm^-1 resolution. The versatility of the optical parametric oscillator as a coherent light source in trace-gas detection is demonstrated with photoacoustic and cavity ring-down spectroscopy. A 17-cm^-1-wide CO₂ spectrum at 2.8 μm and multi-component gas mixtures of methane, ethane and water in human breath were measured using photoacoustics. Methane (at 3.2 μm) and ethane (at 3.3 μm) were detected using cavity ring-down spectroscopy with detection limits of 0.16 and 0.07 parts per billion by volume, respectively. A recording of ¹²CH₄ and ¹³CH₄ isotopes of methane shows the ability to detect both species simultaneously at similar sensitivities. PACS 42.65.Yj; 42.72.Ai; 42.62.Fi     

Electronic and geometric structures of MoxSy and WxSy (x =1, 2, 4; y =1–12) clusters

Electronic and geometric structures of M_xS_y (M = W, Mo; x=1,2,4;y=1–12) clusters have been studied using density functional theory calculations, and compared to experimental photoelectron spectra. For the metal atoms, an uptake of up to six sulfur atoms has been observed, which can be explained by the bonding of S₃ ^- chains. A structural difference to the corresponding oxides is the preference of bridging sites for S, which might be the origin of the differences between the structures of bulk MO₃ and MS₂. For x=1,2 the HOMO–LUMO gaps vary irregularly. For x=4, a large HOMO–LUMO gap has been found for y=6,7, and 8 and the W₄S₆ and Mo₄S₆ clusters have been found to be magic with an extraordinarily high stability. PACS 73.22.-f; 61.46.+w     

Multiwavelength Raman fiber lasers with equalized peak power using a sampled chirped fiber Bragg grating

Two novel multiwavelength Raman fiber lasers using a ring cavity and a linear cavity are proposed and demonstrated experimentally. Both laser configurations include a sampled chirped fiber Bragg grating used in the reflection mode. By adjusting the polarization controller (PC) in the cavities, up to ten stable lasing wavelengths with 0.8 nm spacing and equalized peak power are achieved at room temperature. It is observed that the output spectrum depends upon which port of the grating is connected to the cavity. These two fiber ring lasers offer advantages such as, stable room temperature operation, simple structure, low loss, multiwavelength lasing lines with moderate output power. PACS 42.55.Wd; 42.55.Ye; 42.81.-i     

Spectral shift of a twisted electromagnetic Gaussian Schell-model beam focused by a thin lens

Spectral changes of a twisted electromagnetic Gaussian Schell-model (EGSM) beam focused by a thin lens are investigated by using a tensor method. It is shown that the spectral shift is mainly determined by the degree of polarization, twist phase and correlation coefficients of the initial beam. Generically the blue shift occurs at on-axis points, while the red shift can occur at off-axis points.     

A Mössbauer effect study of the Fe2+x Mn1–x Al Heusler alloys

In this work the Mössbauer spectroscopy has been used to study the magnetic properties of Fe_2?+?x Mn_1???x Al alloys with small deviations of composition from the stoichiometric 2:1:1. The Mössbauer parameters obtained for the L2₁ phase indicate H _hf fields of about 25 T and 30 T at 80 K for Fe atoms at X sites in the ordered X₂YZ structure of the L2₁ full Heusler alloys.