Glass Transition (Tg) and Dielectric Loss in Na2O-Bi2O3-TiO2-P2O5 GLASSES

Thermal and dielectric loss properties of Na₂O-Bi₂O₃-TiO₂-P₂O₅ phosphate glasses, have been studied by the differential scanning calorimetry (DSC) and electrical factor loss (tgi) measurements. The variation of tgi has been followed along two lines inside the quaternary systems Na₂O-Bi₂O₃-5TiO₂-P₂O₅ and Na₂O-5Bi₂O₃-TiO₂-P₂O₅. Experiments have been carried out from ambient temperature to 450°C and show a strong influence of sodium, bismuth and titanium ions on T_g and tgi.     

Multicomponent GeSe2-CdI2-TeO2 (Bi2O3) systems: glass formation and properties

The glass-forming regions of the GeSe₂-CdI₂-TeO₂ (I), GeSe₂-CdI₂-Bi₂O₃ (II) and GeSe₂-TeO₂-Bi₂O₃ (III) systems have been determined. The obtained glassy phases have been characterized by their basic physicochemical parameters such as temperatures of glass transition, crystallization, and melting, density and microhardness. The phase T-X diagram of the GeSe₂-CdI₂ system, which is the basic joint line for systems I and II, has been specified. Three non-variant equilibria (two eutectic and one syntectic) have been observed at temperatures 350, 280 and 375 °C for compositions containing 15, 95 and 33.3 mol% GeSe₂, respectively. A new intermediate phase with probable composition of 2CdI₂·GeSe₂ has been formed.     

Vibrational Excitation of N2(B,C) and N+2(B) States in N2 and N2 – H2 Flowing Microwave Discharges

The ro‐vibrational spectra of N₂ microwave discharges have been analysed by emission spectroscopy. It is deduced the rotational and vibrational temperatures of N₂ states. The characteristic of vibrational temperature Θ₁ of the N₂ (X, v) ground state has been specifically determined.It has been found that the N₂ (C, B, v') and N⁺₂ (B, v') radiative states are directly excited by electron collisions on the N₂ (X,v) ground state at a N₂ gas pressure of 0.1 Torr (discharge tube of 5 mm I.D, microwave power 100 Watt) with a Θ₁ value near 10⁴ K. At higher gas pressure up to 5 Torr, the N₂ (C, v') states remain alone to be mainly excited by electron collisions on N₂ (X, v). It is considered the excitations of the N₂ (B, v') states by collisions of electrons and N₂ (X,v > 4) vibrational molecules on the N₂ (A) metastable states.With x < 9% H₂ into N₂, it is observed an increase of N₂, 2^nd pos intensity, resulting of an increase of high energy electrons. Inversely, the N₂, 1^st pos intensity decreased, partly following the decrease of low energy electrons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of the Ni K-edge X-ray absorption near edge structure in Ni((C2H5O)2PS2)2

The Ni((C₂H₅O)₂PS₂)₂ complex has been investigated using the X-ray absorption near edge structure (XANES) analysis. Nickel K-edge XANES spectra of the complex have been measured and theoretical calculations of the spectra have been carried out using the finite difference method; the calculation of molecular potential has been carried out both in the full potential and in the muffin-tin approximation. The analysis of results obtained has shown that a good agreement between theoretical and experimental spectra in the low-energy region is achieved only in the case of full potential calculations (beyond the muffin-tin approximation for the potential shape).     

Electrochemical sensing of H2O2 using cobalt oxide modified TiO2 nanotubes

Cobalt oxide (Co₃O₄) modified anatase titanium dioxide nanotubes (ATNTs) have been investigated for the electrochemical sensing of hydrogen peroxide (H₂O₂). ATNTs have been synthesized by a two-step anodization process. ATNTs were then modified with Co₃O₄ employing chemical bath deposition method. The structure and morphology of ATNTs and their modification with Co₃O₄ has been confirmed by X-ray diffraction by scanning electron microscopy. H₂O₂ sensing has been studied in 0.1 M PBS solution, by cyclic voltammetry and amperometry. Variation in the peak positions and current densities was observed with addition of H₂O₂ for Co₃O₄ modified ATNTs. Sensitivity and limit of detection improved with modification of ATNTs with Co₃O₄ with precursor concentration up to 0.8 M. However, at higher precursor concentrations sensitivity and limit of detection toward H₂O₂ deteriorated. Co₃O₄ Modified ATNTS using 0.8 M precursor concentration are comparatively more suitable for H₂O₂ sensing applications due to the optimum formation of Co₃O₄/ATNTs heterojunctions.     

Synthesis and properties of HgI2 intercalation of Bi2Sr2CaCu2Oy superconductor

Polycrystalline or single crystals of HgI₂ intercalated Bi₂Sr₂CaCu₂O_y (Bi2212) have been synthesized and their properties have been studied together with those of HgBr₂ intercalates. Single crystals of HgI₂ intercalated Bi2212 were synthesized by a stepwise intercalation method using iodine intercalate as a secondary host material. These could not be obtained through direct intercalation methods by which polycrystalline sample were obtained. From ac susceptibility and resistivity measurements, superconducting onset temperature (T_con) for polycrystalline HgI₂ intercalate was found to be 82 K which was higher than that of the host (75 K). On the other hand, T_con for single crystal HgI₂ intercalate was shown to be 79–80 K which is lower than that of host (95–97 K). The effect of HgI₂ or HgBr₂ intercalation on T_c tried discussion from the view point of hole doping and interblock coupling effect.     

Can (H2O) n (n = 1–2) as effective catalysts in the CH2OO + H2S reaction under tropospheric conditions?

The addition reaction of CH₂OO?+?H₂S → HSCH₂OOH without and with catalyst X (X?=?H₂O and (H₂O)₂) has been investigated by CCSD(T)-F12a/VTZ-F12//B3LYP/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling correction. When H₂O was introduced in the CH₂OO?+?H₂S reaction, it not only acts as a catalyst for producing HSCH₂OOH, but also plays as a reactant to forming HOCH₂OOH. The formation channel of HSCH₂OOH is more important than the formation channel of HOCH₂OOH with its calculated rate constant larger by 11.0–43.2 times within the temperature 280–320?K. Then, (H₂O)₂ catalysed CH₂OO?+?H₂S → HSCH₂OOH reaction has been taken into account with its rate lower 1.9–4.2 times than the reaction of CH₂OO?+?H₂S → HSCH₂OOH with water. Also, CH₂OO?+?H₂S with H₂O cannot compete with the CH₂OO?+?H₂S reaction without water. This is different from CH₂OO?+?(H₂O)₂ reaction, which is about 4 orders of magnitude larger than the rate constant for CH₂OO?+?H₂O reaction. Such discrepancy is possible because C(CH₂OO)···O(H₂O) interaction has been enhanced more obviously by H₂O as compared to that of C(CH₂OO)···O(H₂S) interaction.     

Infrared reflectance spectra and optical conductivity of Tl2CaBa2Cu2O8 and Tl2Ca2Ba2Cu3O10 superconducting thin film samples

Films of the Tl₂CaBa₂Cu₂O₈ (Tl2122 phase) and Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223 phase) superconductors were prepared by d.c. magnetron sputtering method. Their C-axes were perpendicular to the surface. We measured their infrared (IR) reflectivity spectra and assignments of the phonon oscillators were made. The optical conductivity of Tl2122 and Tl2223 phases in the normal state have been obtained from measurements of the reflectivity over a wide frequency range. The position of the plasma peak is tentatively determined.     

Vibrational Spectra and Structure of Potassium Alum Kal(SO4)2·12[(H2O) x (D2O)1−x ]

The IR spectra and polarization Raman spectra of Kal(SO₄)₂·12(H₂O) and Kal(SO₄)₂·12[H₂O)_0.3(D₂O)_0.7] crystals at 93 K and room temperature have been obtained experimentally. The vibrational spectra of structural elements of potassium alum — the complexes [Al(H₂O)₆ ³⁺ and [Al(D₂O)₆]³⁺ — have been calculated. The vibrational spectra have been interpreted based on the calculation and factor-group analysis data. The spectral data obtained point to the fact that, in the crystals considered, the sulfate ions are partially disordered and there exist two crystallographically different types of water molecules.     

Mechanism of Bi2Sr2CaCu2Ox crystallization and superconducting properties for Bi2Sr2CaCu2Ox/Ag tapes prepared using isothermal partial melting method

The mechanism of Bi₂Sr₂CaCu₂O_x (Bi-2212) crystallization from a partially molten state has been studied by means of thermal analysis, X-ray diffraction (XRD) measurement, and microstructural observation in Bi-2212/Ag tapes. Tapes have been prepared using the isothermal partial melting (IPM) method, under which partial melting and solidification are carried out at the same temperature in an nitrogen atmosphere and 20% oxygen partial pressure (p(O₂)), respectively. The Bi-2212 phase crystallizes by peritectic reaction between (Sr, Ca)CuO₂ (1:1 phase) and the liquid phase at processing temperatures (T_p)≥855°C. At the beginning of Bi-2212 crystallization, only the 1:1 and the liquid phases are present in tapes. The Bi-2212 nucleation occurs in the vicinity of 1:1 grains (homogeneous nucleation). This peritectic reaction progresses by recovery of oxygen in the liquid phase. In contrast, the nucleation of the Bi-2212 phase occurs heterogeneously at T_p≤850°C. The Bi-2212 phase co-exists with four Bi-free phases ((Sr, Ca)₁₄Cu₂₄O₄₁ (14:24 phase), (Sr, Ca)₂CuO₃ (2:1 phase), (Sr, Ca)O (1:0 phase), and the 1:1 phase) and the liquid phase in the early stage of the Bi-2212 crystallization step. Since the precipitation temperature of the Bi-2212 phase is higher than 850°C, the Bi-2212 crystallization progresses by direct precipitation. The crystallization paths affect microstructure and transport critical current density (J_c) of Bi-2212 tapes.     

Electronic Emission from Hg-Atoms and HgCl-Radicals Due to Collisions of Nitrogen Ions and HgCl2/Hg2Cl2 Molecules

Emission spectra of the (B-X), (C-X) and (D-X) band systems of HgCl-radical and mercury atomic lines from highly excited levels to various lower levels have been observed during collisions of N⁺ and N⁺ ₂ ions and HgCl₂/Hg₂Cl₂ molecules at different laboratory kinetic energies of the projectile ions. Emission cross-sections of the most intense mercury atomic lines and the (C-X) band system of the HgCl-radicals, have been measured in the laboratory kinetic energy range of 100–900 eV.     

Melt synthesis and structural properties of opal-V2O5 and opal-VO2 nanocomposites

A method has been proposed for filling bulk and film opals with V₂O₅ and V₂O₅: W melts under the action of capillary forces. The VO₂ and VO₂: W (1.8 mol %) compounds have been synthesized from the V₂O₅ and V₂O₅: W precursors in opal pores. The phase composition and morphology of the nanocomposites prepared have been investigated. It has been revealed that, in the opal-V₂O₅ composite, the filler compound has a texture formed by the directional crystallization of the melt in pores of the opal film. The tunable photonic crystal heterostructure opal/opal-VO₂ has been synthesized using liquid chemical etching.     

Hyperfine interactions for181Ta nuclei in the laves phases LuFe2 and GdFe2

The hyperfine magnetic fields for¹⁸¹Ta in the cubic (C 15) Laves phases LuFe₂ and GdFe₂ have been measured by the TDPAC method. At 300 K, B_hf=−20.5(4) T for LuFe₂ and +19.0(5) T and +10.2(4) T for the samples of GdFe₂, prepared at normal and high (7.7 GPa) pressure, have been obtained. Temperature dependence of these fields in the range 77–900 K has been also measured.     

Tetragonally distorted Cr2+ ions in BaF2 and SrCl2 studied by ESEEM spectroscopy

Electron spin echoes on tetragonally distorted non-Kramers Cr²⁺ ions in chromium doped BaF₂ and SrCl₂ single crystals have been observed. The superhyperfine interaction (shf) with the nearest halide ions has been studied using the electron spin echo envelope modulation (ESEEM) signal. For Cr²⁺ in BaF₂ the nearest coordination shell consists of four equivalent fluorine ions in a plane perpendicular to the defect tetragonal axis, the Cr²⁺ ion being off-centre displaced towards the fluorine plane. The Cr²⁺ shf tensor for BaF₂ has been determined. For SrCl₂:Cr ESEEM signals associated to the shf interaction with nearest chloride ions were observed but the measurements did not allow us to give a definitive defect model in this case.     

Electrochemical comparison between SnO2 and Li2SnO3 synthesized at high and low temperatures

Li₂SnO₃ has been synthesized at 1000 °C from Li₂CO₃ and SnO₂ (high temperature form - HT) and it has also been prepared from ball-milled SnO₂ and Li₂CO₃ at 650 °C (low temperature form - LT). The Li₂SnO₃ materials have been tested as a negative electrode for possible use in a Li-ion cell and their electrochemical behaviour has been compared with that of SnO₂. In theory, Li₂SnO₃ and SnO₂ should be able to cycle the same number of lithium atoms per tin atom but on the initial discharge SnO₂ has inserted more lithium than Li₂SnO₃. During the initial discharge of SnO₂ and Li₂SnO₃, a side electrochemical reaction seems to be occurring. The resultant compound apparently inserts lithium reversibly for potentials around 1 V; however, cycling from 0.02–2 V significantly degrades performance compared to 0.02–1 V. Li₂SnO₃ (HT) allows the de-insertion of more lithium than Li₂SnO₃ (LT) and SnO₂ in the first charge. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Performance improvement of phase-change memory cell with Ge2Sb2Te5-HfO2 composite films

The phase-change characteristics of Ge₂Sb₂Te₅ (GST) films for phase-change random access memory (PCM) devices were improved by incorporating HfO₂ into GST film using cosputtering at room temperature. Phase separation (GST-rich nanocrystals were surrounded by HfO₂-rich amorphous phase) has been observed in annealed GST-HfO₂ composite films and the segregated domains exhibited a relatively uniform size. The reduced reset voltage of GST-HfO₂ based cell was due to the reduced programming volume by incorporating HfO₂ into GST. This work clearly reveals the highly promising potential of GST-HfO₂ composite films for application in PCM.     

Infrared Spectrum of Pyromellitic Diimide HN(CO)2C6H2(CO)2NH

The IR spectrum of pyromellitic diimide, HN(CO)₂C₆H₂(CO)₂NH, has been measured for polycrystalline sample. The observed bands have been assigned to the IR active fundamentals and combinations on the basis of a D_2h molecular symmetry by comparison with those of pyromellitic dianhydride. Band shifts from dianhydride to diimide were observed for the 0[dbnd]C-X-C[dbnd]O fundamentals and the N-H modes have been assigned by comparison with those reported for phthalimides.     

Anomalous diamagnetic transitions in Ba2Cu3O4Cl2 and Sr2Cu3O4Cl2 antiferromagnets

The magnetic properties of Ba₂Cu₃O₄Cl₂ and Sr₂Cu₃O₄Cl₂ oxychlorides have been studied. A spontaneous manifestation of diamagnetism has been found at quasi-zero and low fields. The temperature of these transitions coincides with the temperature of the antiferromagnetic ordering in Ba₂Cu₃O₄Cl₂ (T _NI ≈ 337 K) and Sr₂Cu₃O₄Cl₂ (T _NI ≈ 386 K). The recorded diamagnetic signal is ?10^?4 emu. It is comparable with the percentage of the superconducting phase in the sample. It is supposed that the arising superconductivity is due to the formation of the superconducting clusters with the direct overlap of the copper d orbitals owing to the frustration processes.     

Superconductivity in CeCu2Si2

Resistivity measurements of CeCu₂Si₂ are carried out under pressures p up to 12 kbars. Unlike polycrystalline samples, no traces of superconductivity have been observed in CeCu₂Si₂ at ambient pressure. When pressure is applied, CeCu₂Si₂ monocrystals become superconducting with anomalously large ratio H_c2(0)/T_c (0) = 34 K0e/K and with the derivative dH_c2/dT(T=T_c) = 140 K0e/K