Magnetic properties of Nd0.9Dy0.1Fe3(BO3)4

The magnetic properties of trigonal Nd_0.9Dy_0.1Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.9Dy_0.1Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 8 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B‖c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.9Dy_0.1Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.     

Features of the magnetic and magnetoelectric properties of HoAl3(BO3)4

The main features of the magnetic and record magnetoelectric properties of a HoAl₃(BO₃)₄ aluminoborate single crystal have been studied experimentally and theoretically. It has been found that the electric polarization that was previously detected in HoAl₃(BO₃)₄ and is record for multiferroics is significantly larger, ΔP _ba (B _a ) ≈ ?5240 μC/m², with an increase in the magnetic field to 9 T at T = 5 K. The measured magnetic properties and revealed features have been interpreted within a united theoretical approach based on the molecular field approximation and on calculations in the crystal field model for a rare-earth ion. The experimental temperature (from 3 to 300 K) and field (up to 9 T) dependences of the magnetization have been described. The parameters of the crystal field of trigonal symmetry for a Ho³⁺ ion in HoAl₃(BO₃)₄ have been determined from the interpretation of the experimental data.     

Electrochemical lithium incorporation into WO3 and MoO3 thin films

The generally accepted mechanism of electrochromic phenomena into WO₃ thin films involves the simultaneous injection of cations and electrons to form a tungsten bronze M_xWO₃, e.g. H_xWO₃,Li_xWO₃. Electrochromic cells of the type ITO MO₃/LiClO₄(M) in propylene carbonate/Pt, where M = W or MO and MO₃ is an amorphous thin film have been used. Different amounts of charges have been injected through these cells by electrochemical means at room temperature. The variations of the MO₃ electrode potential with the injected charge are in good agreement with the assumption of the formation of Li_xMO₃ compounds. The free enthalpies of formation of these bronzes have been calculated. The behavior of thin film electrodes seems to be intermediate between amorphous and crystallized bulky materials. Some measurements of electrode potential have also been carried out with crystallized thin films of sputtered WO₃.     

Availability of water glass/Bi2O3 composites in dielectric and gamma-ray screening applications

ABSTRACT

Sodium silicate (Na₂Si₃O₇) also known as water glass is a very low cost material which is used in many industrial applications such as a builder in detergents, as a binder and adhesive etc. But so far the electrical properties of sodium silicate and its ability to screen radiation have never been investigated. In the present study, the frequency dependent electrical properties and gamma-ray shielding performance of water glass based bismuth oxide composites have been studied for the first time. In accordance with this purpose, Na₂Si₃O₇/Bi₂O₃ glassy composites have been prepared for searching their possible applications in electronics and radiation screening. The surface morphology of the samples have been determined by Scanning Electron Microscope (SEM). The frequency dependent electrical properties such as complex impedance, complex dielectric function and conductivity have been analyzed at room temperature between 1 and 40?MHz. As a result of alternative current (ac) electrical analysis, it has been determined that the Na₂Si₃O₇/Bi₂O₃ composites can be utilized as a dielectric layer in capacitors. On the other hand, since bismuth oxide is an anti-radiative material, the gamma-ray screening parameters such as mass attenuation coefficient, half layer and tenth layer values along with mean free path of the composites have been defined experimentally by using NaI(Tl) scintillation detector for the Ba-133 radiation source at 81 and 356?keV. The values of these parameters have also been checked by Monte–Carlo simulation. Since a good agreement has been assigned between experimental and Monte–Carlo simulation results, the related gamma ray shielding parameters have been determined by Monte–Carlo simulation for other gamma photon energies (140?keV, 208?keV, 468?keV, and 661?keV) which are generated from Tc-99, Lu-177, Ir-132, and Cs-137 sources. Ultimately, Na₂Si₃O₇/Bi₂O₃(35%) composite has been suggested as an eco-friendly, lead-free glassy structured material for the gamma radiation shielding in medical applications.     

Optical properties of Nd3+ pairs in LiYF4-existence of a short range interaction

Optical studies of Bridgman grown LiYF₄ crystals weakly doped with Nd³⁺ have been made in the vicinity of the ⁴I_9/2→⁴G_5/2 transition. By selective excitation with a narrow pulsed laser or with a CW monomode laser, excitation spectra and dynamical characteristics of infrared and ultraviolet (up-converted) fluorescences produced by satellites associated with Nd³⁺ pairs have been obtained. From the results, an assignment of the satellites to the various classes of pairs has been possible. The existence of a short range interaction, probably superexchange, has been proved which confirms previous observations in another fluoride compound, LaF₃.     

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract

The high resolution (0.0010cm^?1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH₂DI and CHD₂1 have been recorded and analysed in the ν₃ band regions around 510cm^?1. The fundamental band ν₃ is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH₂DI and CHD₂I, respectively. About 4700 transitions in the case of CH₂DI and about 3900 transitions in the case of CHD₂I have been assigned. The ground state rotational constants of CH₂DI and CHD₂I have been obtained using the ground state combination differences calculated from the assigned ν₃ transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v₃=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH₃I and CD₃I     

Structural, electrical and gas-sensing properties of In2O3 : Ag composite nanoparticle layers

The central objective of this study is to investigate (i) size-dependent properties of In₂O₃ nanoparticles and (ii) the role of metal additives in enhancing the gas sensing response. For this purpose, In₂O₃ : Ag composite nanoparticle layers having welldefined individual nanoparticle size and composition have been grown by a two step synthesis method. Thermogravimetric analysis, X-ray diffraction and transmission electron microscopy have been used to study the effect of post-synthesis heat treatment on the size and structure of the nanoparticles. A first-time unambiguous observation of sizedependent lowering of transformation temperature has been explained in terms of lower cohesive energy of surface atoms and increase in surface-to-volume ratio with decrease in nanoparticle size. The gas sensing studies of In₂O₃ as well as the In₂O₃ : Ag composite nanoparticle layers have been studied as a function of size and composition. In₂O₃: Ag composite nanoparticle layers with 15% silver show a sensitivity of 436 and response time of 6 s for 1000 ppm of ethanol in air. Ag additives form a p-type Ag₂O, which interact with n-type In₂O₃ to produce an electron-deficient space-charge layer. In the presence of ethanol, interfacial Ag₂O reduces to Ag, creating an accumulation layer in In₂O₃ resulting in increased sensitivity     

Mössbauer investigations of Fe and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles for hyperthermia applications

Magnetic nanoparticles of magnetite Fe₃O₄ and Fe synthesized by physical vapor deposition with a fast highly effective method using a solar energy have been studied. Targets have been prepared from tablets pressed from Fe₃O₄ or Fe powders. Relationships between the structure of nanoparticles and their magnetic properties have been investigated in order to understand principles of the control of the parameters of magnetic nanoparticles. Mössbauer investigations have revealed that the nanoparticles synthesized from tablets of both pure iron and Fe₃O₄ consist of two phases: pure iron and iron oxides (γ-Fe₂O₃ and Fe₃O₄). The high iron oxidability suggests that the synthesized nanoparticles have a core/shell structure, where the core is pure iron and the shell is an oxidized iron layer. Magnetite nanoparticles synthesized at a pressure of 80 Torr have the best parameters for hyperthermia due to their core/shell structure and core-to-shell volume ratio.     

Crystallographic and optical properties of rare-earth chromium sulfides RCrS3

Rare earch chromium sulfides RCrS₃; R=Y, Gd, Dy, Ho and Er have been synthesized by high temperature reaction of the respective oxides, RCrO₃, with CS₂. Single crystals have been grown by mineralization of the polycrystalline powders using halogen as a mineralizer. The crystal structures were determined from X-ray rotation and Weissenberg photographs. RCrS₃, with R=Y, Gd, Ho and Er, were found to have an isostructural monoclinic structure, while DyCrS₃ was found to have an orthorhombic structure, closely related to the monoclinic compounds. The optical absorption of these compounds, as well as of LaCrS₃ whose structure was previously reported, was measured over the photon energy range 0·15～1·7 eV. For all the compounds, a sharp absorption edge was found at 1·20～1·30 eV at room temperature.This absorption edge shifts toward higher energy upon cooling from room temperature. The infrared absorption of DyCrS₃, HoCrS₃ and ErCrS₃ was negligible, while that of YCrS₃, LaCrS₃ and GdCrS₃ increased markedly, with decreasing photon energy.     

The high-resolution infrared spectra of the ν2 and ν3 bands of HOCl

The infrared spectra of the a-type transitions of the ν₂ and ν₃ bands of HO³⁵Cl and HO³⁷Cl have been obtained under high resolution. Line assignments of both bands have been made, and the spectroscopic constants have been obtained for both bands using a Watson Hamiltonian. Lines of the K_a = 5 subband of the ν₂ band of the HO³⁵Cl molecule were found to be slightly shifted by an interaction with the K_a = 4 level of the 2ν₃ vibrational state. The b-type transitions permitted for both bands were too weak to observe. Relative intensities of selected lines of both bands have been measured, and empirical Herman-Wallis factors have been determined.     

Atomic Absorption Spectrometry of Fire-Extinguishing Aerosols

The process of extinguishing a propane-air flame by aerosols of salt solutions has been investigated with the use of an atomic absorption spectrometer. The method of comparing aerosols in terms of the extinguishing efficiency has been evaluated. The changes in the flame temperature and spectra at different jet heights under the influence of aerosols of water and K₂CO₃ and Al(NO₃)₃ solutions have been shown.     

Magnetic properties and surface morphology of layered In2Se3 crystals intercalated with cobalt

The magnetic properties of layered Co _x In₂Se₃ crystals electrochemically intercalated with cobalt in an external magnetic field and without a magnetic field and the morphology of the van der Waals surfaces of layers of these crystals have been investigated. It has been found that the ferromagnetic ordering at room temperature is observed only for Co _x In₂Se₃ crystals intercalated in an external magnetic field. These crystals are nanocomposite materials that consist of a layered matrix and arrays of nanorings and nanowires formed from Co nanocrystals on the van der Waals surfaces of the In₂Se₃ layers. Cobalt nanocrystals in Co _x In₂Se₃ crystals have a pyramidal equilibrium shape, which is characteristic of the face-centered cubic crystal structure, and their geometrical sizes are of the order of a few nanometers. The specific features of self-organization of cobalt magnetic nanostructures on the van der Waals surfaces of layered semiconductor crystals during their electrolytic intercalation in a magnetic field and the magnetic properties of these structures have been considered.     

The molecular structure and the analytical potential energy function of S2^- and S3^-

In this paper, the equilibrium geometry, harmonic frequency and dissociation energy of S2^- and S3^- have been calculated at QCISD/6-311＋＋G（3d2f） and B3P86/6-311＋＋G（3d2f） level. The S2^- ground state is of 2IIg, the S3^- ground state is of 2B1 and S3^- has a bent （C2v） structure with an angle of 115.65° The results are in good agreement with these reported in other literature. For S3^- ion, the vibration frequencies and the force constants have also been calculated. Base on the general principles of microscopic reversibility, the dissociation limits has been deduced. The Murrell-Sorbie potential energy function for S2^- has been derived according to the ab initio data through the least- squares fitting. The force constants and spectroscopic data for S2^- have been calculated, then compared with other theoretical data. The analytical potential energy function of S3^- have been obtained based on the many-body expansion theory. The structure and energy can correctly reappear on the potential surface.     

Atomic force microscopy studies of SrTiO<Subscript>3</Subscript> (001) substrates treated by chemical etching and annealing in oxygen

The SrTiO₃ (001) substrates treated by chemical etching in NH₄F-buffered HF solution and annealing in oxygen ambient have been studied by an atomic force microscopy (AFM). The SrTiO₃ substrates with TiO₂-termineted and atomically smooth surfaces and single unit cell steps have been obtained. The surface morphologies of SrTiO₃ substrates strongly depend on the treated conditions and the quality of the substrates.     

EPR spectra of a GdMnO3 thin film on a SrTiO3 substrate

Electron paramagnetic resonance (EPR) spectra of a GdMnO₃/SrTiO₃ thin film in the X band have been measured in the temperature interval from 200 to 450 K. Signals from two types of paramagnetic centers have been observed in the spectra. The first paramagnetic center is a subsystem of Gd³⁺ ions, in the EPR spectrum of which the fine structure lines are resolved below 350 K. The second paramagnetic center is a system of manganese and gadolinium ions, in the EPR spectrum of which an exchange-narrowed line is observed with the width ΔH several times less than the width ΔH of an exchange-narrowed line observed in the GdMnO₃ single crystal. Unusual magnetic properties are due to the mismatch of the lattice parameters of the GdMnO₃ thin film and the SrTiO₃ substrate.     

New optically-pumped lasers containing silicon

Fifty-five FIR laser lines, generated by optical pumping with various isotopically-labelled CO₂ lasers, have been observed from SiH₃F, SiH₂F₂ and SiHF₃. Eleven of the lines from ²⁸SiH₃F have been assigned with the aid of available spectroscopic data and an accurate calculation of the vibration-rotation spectrum around 10 μm.     

Preparation of conventional thermoelectric nanopowders by pulsed laser fracture in water: application to the fabrication of a pn hetero-junction

The technique of laser fracture in a liquid medium has been applied to the synthesis of n-type (Bi_0.95Sb_0.05)₂ (Te_0.95Se_0.05)₃ and p-type (Bi_0.2Sb_0.8)₂Te₃ semiconducting nanopowders which are the best conventional materials currently used for thermoelectric applications at ambient temperature. The nanopowders have been prepared with a high yield in an especially built-up cell. Laser fracture in water of micronsized powders has been applied, using a nanosecond Nd:YAG laser working at 532 nm. The obtained powders have been characterized by scanning and transmission electron microscopy and by X-ray diffraction. The mean diameter is about 10 nm and the phase of the initial powders is kept. To test the potentiality of these nanosized materials, we have shown the feasibility to produce a pn hetero-junction.     

Prediction of the inversion splittings of the nv 2 vibrational levels in phosphine (PH3, PD3 and PMu3)

Inversion splittings of the nv ₂ vibrational levels in PH₃ and PD₃ have been calculated using a theoretical model developed by us for molecular inversion in XY₃ pyramidal molecules and the slightly modified results of an ab initio SCF-LCAO-MO calculation of the double minimum potential function for PH₃ by Lehn and Munsch. Inversion splittings have been predicted also for the chemical compound PMu₃, where Mu is muonium.     

Magnetic-field induced coupling of quasi-degenerate phonon modes in the rare-earth compounds TmVO4 and TbF3

In this work the effects of magnetoelastic interaction in Rare-Earth compounds between excited crystal field states and nondegenerate optical phonons have been studied in tetragonal TmVO₄ and in orthorhombic TbF₃, using Raman and far-infrared spectroscopy. In certain favourable cases a mutual energy renormalization of the phonons has been observed as a function of a magnetic field (TmVO₄) or depending on the direction of the spontaneous magnetization of the crystal (TbF₃).In magnetically ordered TbF₃ an effective phonon-phonon coupling between modes of pure transverse and longitudinal polarization has been studied. This interaction results in an elliptical polarization of the coupled polar modes and transfers transition intensity to the quasi-longitudinal modes.The observed phenomena have been treated theoretically in full agreement with the experiments as higher order effects using the well established theory of magnetoelastic effects.