Raman spectroscopic study of the uranyl titanate mineral holfertite Ca x U2−x Ti(O8−x OH4x )·3H2O and the lack of metamictization

Raman spectra of the uranyl titanate mineral holfertite Ca _x U_2?x Ti(O_8?x OH_4x )·3H₂O were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO₂)²⁺ stretching and bending vibrations, U–OH bending vibrations, and H₂O stretching and bending. The mineral holfertite is metamict, as is evidenced by the order/disorder of the mineral. Unexpectedly, the Raman spectrum of holfertite does not show any metamictization. The intensities of the UO stretching and bending modes show normal intensity and the bands are sharp.     

Rovibrational spectra of the Ar–D2O and Kr–D2O van der Waals complexes in the v2 bend region of D2O

Rovibrational spectra of Ar–D₂O and Kr–D₂O complexes are measured in the v₂ bend region of D₂O monomer using a tunable mid-infrared diode laser spectrometer. One para and two ortho bands for both complexes are identified and then analyzed in terms of a nearly free internal rotor model. Molecular constants for the excited vibrational states, including band-origin, rotational and centrifugal distortion constants, and Coriolis coupling constant, are determined accurately. A comparison of the observed band-origins of Ar–D₂O and Kr–D₂O with the previous results of Ne–D₂O shows regular trends of shift from Kr–D₂O to Ne–D₂O.     

Nature of the anomalies of the thermolumenescence properties of dosimetric α-Al2O3 crystals

The results of investigations into the anomalies of the thermoluminescence properties of dosimetric corundum crystals are presented. The decisive role of deep-lying traps in the quenching of luminescence in anion-defect Al₂O₃ monocrystals is shown. The existence of deep-lying traps is demonstrated by the method of direct observations of thermoluminescence (TL) peaks associated with them. Experimental evidence for the influence of the degree of occupation of deep-lying traps on the main features of the TL dosimetric peak at 450 K is given. The results obtained are interpreted for a model of the interactive system of traps, which differs radically from the models described in the literature by a consideration of the temperature dependence of the probability of trapping of charge carriers on deep-lying traps. We believe that the heat quenching of luminescence is due to the thermal ionization of excited F-center states. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebhykh Zavedenii, Fizika, No. 3, pp. 55–65, March, 2000.     

The role of surface hydroxils of Al2O3·xH2O in the luminescence of adsorbed fluorescein molecules

Acta physica Academiae Scientiarum Hungaricae - Producing various surface hydroxil concentrations on Al2O3 films by surface reactions it was found that there is a distinct relation between the...     

Investigation of the GdMn2O5 multiferroic by the μSR method

The GdMn₂O₅ multiferroic (a ceramic sample and a sample consisting of a large array of randomly oriented single crystals with linear dimensions 2–3 mm) has been studied by the μSR method within the temperature range 10–300 K. Three anomalies in the temperature behavior of the parameters of the muon polarization relaxation function, namely, close to the phase transition driven by the onset of long-range magnetic order in the manganese ion subsystem (T _N1 = 40–41 K), near the lock-in transition initiated by an abrupt change of the wave vector of magnetic order (T _L = 35 K), and close to the Gd³⁺ ion ordering temperature (T _N2 = 15 K), have been found. An analysis of the time spectra of muon spin precession in the internal magnetic field of the samples has revealed two positions of preferable muon localization sites in samples, which differ in precession frequencies and the character of their behavior with temperature. The lower-frequency precession driven by Mn⁴⁺ ions, ferromagnetic Mn4⁺-Mn⁴⁺ + muonium complexes, and Gd³⁺ions is observed throughout the temperature region T < T _N1 and is practically independent of temperature. At temperatures T < T _L = 35 K, a higher-frequency precession associated with Mn³⁺ ions appears also. It is characterized by a temperature dependence ～(T/T _N1)^β with the index β = 0.39, which is typical of Heisenberg-type 3D magnets. For T < T _N1, a deficiency of the rest total asymmetry is observed. This phenomenon can probably be assigned to formation of muonium, which suggests that charge transfer processes play an important role in formation of long-range magnetic order.     

Activation energy and conductivity of glasses in the P2O5–V2O5–Li2O system

The conductivity of glasses in the 50\textP_\text2 \textO_\text5 - x\textV_\text2 \textO_\text5 - ( 50 - x )\textLi_\text2 \textO50{\text{P}}_{\text{2}} {\text{O}}_{\text{5}} - x{\text{V}}_{\text{2}} {\text{O}}_{\text{5}} - \left( {50 - x} \right){\text{Li}}_{\text{2}} {\text{O}} system was studied as a function of temperature and composition. For all compositions, the conductivity variation as a function of temperature followed an Arrhenius type relationship. Isothermal variation of conductivity as a function of composition showed a minimum for a molar ratio x near 20. Probable mechanisms for decrease of conductivity with decrease of vanadium oxide concentration were explained. The minimum in room temperature was attributed to increase of V⁴⁺/V⁵⁺ with decrease of vanadium oxide in specific concentrations of vanadium oxide. Activation energy increased with decrease of V₂O₅ content. This behavior was attributed to increase of average spacing between vanadium ions.     

Vibrational spectroscopic characterization of the magnesium borate-phosphate mineral lüneburgite

ABSTRACT

Lüneburgite, a rare magnesium borate-phosphate mineral from Mejillones, Chile, has been characterized using Raman and mid-infrared spectroscopy methods. Boron tetrahedra are characterized by sharp Raman band at 877?cm^?1, attributed to the ν₁[BO₄]^5? symmetric stretching mode. The phosphate anion is associated with a distinct band at 1032?cm^?1, attributed to the ν₃[PO₄]^3? antisymmetric stretching mode. The most intensive Raman band at 734?cm^?1 is ascribed to stretching vibrations of bridging oxygen atoms in boron–oxygen–phosphor bridges. Bonds associated with water bending mode and stretching vibration are observed at 1661?cm^?1 (infrared) and in the 3000–3500?cm^?1 region (Raman and infrared spectrum).     

Effect of the Coadsorption of CO and O2 on the Phase Diagram of the Ziff—Gulari—Barshad Model

The effect of the coadsorption of CO and O2 on the Ziff-Gulari-Barshad surface catalytic reaction system in studied by Monte Carlo simulation.The coadsorption of both species adds an extra reaction step to the classical Ziff-Gulari-Barshad model.It is shown that the second-order phase transition from the reactive state to the O-passivated state in the Ziff-Gulari-Barshad model is eliminated,and the production rate of CO2 increases linearly along the fraction yco of CO in gas phase when it is low,in agreement with experimental results.We also find that the increase of the probability of the coadsorption leads to the decrease of the critical value of yco of the discontinuous phase transition to the CO-passivated state.     

Energy-dependent enhancement of the electron-coupling spectrum of the underdoped Bi2Sr2CaCu2O(8+δ) superconductor

We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O(8+δ) from high-resolution angle-resolved photoemission spectra by two deconvolution-free robust methods. As hole concentration decreases, the coupling spectral weight at low energies ?15 meV shows a twofold and nearly band-independent enhancement, while that around ～65 meV increases moderately, and that in ?130 meV decreases leading to a crossover of dominant coupling excitation between them. Our results suggest the competition among multiple screening effects, and provide important clues to the source of sufficiently strong low-energy coupling, λ(LE)≈1, in an underdoped system.     

Specific Features of the Local Structure and Transport Properties of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 Crystals

Optics and Spectroscopy - The specific features of the local structure of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 crystals are revealed by optical spectroscopy using the Eu3+...     

Study of the effect of the substitution of O by F,S, and Cl on the superconductivity of Y1Ba2Cu3O7−δ

We have studied the superconducting transitions of Y₁Ba₂Cu₃D _x O_7–x– samples where O has been replaced by D=F, S, or Cl andx=0.2-2. No single phase compounds were obtained forx>0.2. No dramatic increase inT _c was registered. Generally the results can be interpreted as a dilution of the highT _c 1 2 3 phase by other phases as the dopant concentration increases, ultimately suppressingT _c completely. Possibly there is an increase ofT _c for an intermediate dopant range,x, in the Cl series.     

FT-IR Study of the Adsorption of Propane and Propene on V2O5/γ-Al2O3 Catalyst

It has been observed on the oxidized V₂O₅/γ-Al₂O₃ that C₃H₆ form alkoxides which were converted to acetone during the desorption of adsorbate phase at 373 K. C₃H₈ may form π-complexes on the reduced form of the same catalyst. However, the intensities of the bands in the ad-adsorption of C₃H₈ were very weak as compared with the case of C₃H₈ adsorption. Therefore, it was not reasonable to assign these bands clearly as any of the surface type species.     

Effect of TiO2 addition on the crystallization of quenched glasses in the SiO2–Al2O3–ZrO2 system

The glass formation in the SiO₂-rich region of the ternary oxide system Al₂O₃–ZrO₂–SiO₂ with MgO, CaO, and TiO₂ as melting aids was analyzed. The crystallization of glasses with different content of TiO₂ and phase evolution with the temperature was studied by X-ray diffraction, infrared, laser Raman spectroscopy and transmission electron microscopy. The use of TiO₂ favored formation and crystallization of the glasses due to the decrease of the viscosity of melts and acting as a nucleating agent. The crystalline phase of t-ZrO₂ was developed at temperatures as low as 880°C whereas in as prepared specimens without TiO₂ its presence was not detected. For the specimens with TiO₂, t-ZrO₂ and mullite were the principal phases at 1000°C. TiO₂ addition did not change the crystallization sequence but decreased the formation temperature of the crystalline phases. Most of Ti⁴⁺ ions entered into t-ZrO₂ and only a small portion in mullite, but the surplus was detected in ZrTiO₄.     

Optical properties of glasses in the Li2O–MoO3–P2O5 system

Glasses xLi₂O–(50-x)(MoO₃)₂–50P₂O₅ with x = 10, 20, 30, and 40 mol% were prepared and their optical and electrical properties were investigated. Analysis of the IR spectra revealed that the Li⁺ ions act as a glass modifier that enter the glass network by breaking up other linkages and creating non-bridging oxygens in the network. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films and the optical absorption spectra of those were recorded in the range 200–800 nm. From the optical absorption edges studies, the optical band gap (E _opt) and the Urbach energy (E _e) values have been evaluated by following the available semi-empirical theories. The linear variation of (αhν)^1/2 with hν, is taken as evidence of indirect interband transitions. The E _opt values were found to decrease with increasing Li₂O content by causing increase in the number of non-bridging oxygens in network. The Urbach tail analysis gives the width of localized states between 0.48 and 0.74 eV.     

Control of Crystallization Kinetics and Study of the Thermal, Structural and Morphological Properties of an Li2O–B2O3–Al2O3 Vitreous System

A glass matrix with nominal composition 50Li₂O·45B₂O₃·5Al₂O₃ (mol%) was synthesized, and its physical properties were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and atomic force microscopy (AFM). The glass transition temperature T _g, the crystallization-onset temperature T _x,, the crystallization peak temperatures T _c1 and T _c2, and the fusion peak temperatures T _m1 and T _m2 were determined from at least two glass matrix phases to be approximately 382, 457, 486, 574, 761, and 787?°C, respectively, at 5?°C/min heating rate. Heat treatments at 450?°C for an increasing sequence of time intervals allowed control over the amount of crystallization. Additional information on the crystallization kinetics for the LBA glass matrix was gathered from AFM images, DTA thermograms, and XRD diffractograms. The latter technique showed that LiBO₂ (ICDD-16568) and Li₃AlB₂O₆ (ICDD-51754) phases are formed in the glass?Cceramic system. Debye?CScherrer analysis of the XRD peaks revealed a competition between the evolutions of crystal phases during heat treatment. Activation energies for crystallization, obtained from theoretical models applied to the DTA data showed that the crystallization is heterogeneous. The AFM images demonstrated that this heterogeneous crystallization starts at the surface of the LBA glass matrix and identified crystal sizes in agreement with the results of the Debye?CScherrer analysis. Our study shows that thermal and structural characterization techniques can be combined with theoretical results drawn from well-tested models to offer a unified view of crystallization in a glass?Cceramics system.     

Adsorption and dehydrogenation of 2-propanol on the surface of γ-Al2O3-supported gold

The adsorption and reactions of 2-propanol on γ-Al₂O₃ and γ-Al₂O₃-supported gold samples were investigated by infrared (IR) spectroscopy, modulated differential scanning calorimetry (MDSC) and mass spectrometry. Adsorption of the alcohol on the samples at room temperature led to formation of molecularly adsorbed 2-propanol and 2-propoxide species bonded to Al³⁺ sites. Treatment of γ-Al₂O₃ after alcohol adsorption in flowing He from 25 to 300 °C led to 2-propanol desorption, without evidence of surface reactions. In contrast, when supported gold samples were exposed to the same thermal treatment, formation of acetone and H₂ was observed by mass spectra of the effluent gases from the flow reactor. Concomitantly, IR spectra of the samples showed the appearance of a band at 1698 cm^? 1, assigned to ν_CO vibrations of adsorbed acetone. The formation of acetone occurred by the dehydrogenation of 2-propoxide species bonded to Al³⁺ sites, as evidenced by (a) the decrease in the intensities of their IR bands and (b) the presence of a MDSC peak at approximately the same temperature as that at which acetone was formed and the 2-propoxide species were consumed. It is proposed that gold particles on the γ-Al₂O₃ surface facilitate breaking of the β-CH bond of neighboring surface 2-propoxide species to give acetone. Our results emphasize the bifunctional character of supported gold catalysts for the dehydrogenation of alcohols.     

Infrared diode laser spectroscopy of the Kr–N2O van der Waals complex: the v 1 symmetric stretch region of N2O

The rovibrational spectra of four isotopomers of the Kr–N₂O van der Waals complex, namely ⁸²Kr–N₂O, ⁸³Kr–N₂O, ⁸⁴Kr–N₂O and ⁸⁶Kr–N₂O, were measured in the v ₁ vibrational band region of the N₂O monomer (～1285?cm^?1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. Rotational constants for both ground and excited vibrational states of these four isotopomers were accurately determined. The band-origin of Kr–N₂O was observed to shift by +0.1065?cm^?1 from that of the monomer. The band-origin shifts of Rg–N₂O (Rg?=?Ne, Ar, Kr) in the v ₁ vibrational band region could also be well explained by the model based on a Buckingham intermolecular potential [W.A. Herrebout, H.-B. Qian, H. Yamaguchi and B.J. Howard, J. Mol. Spectrosc. 189, 235 (1998)]. But the band-origin shift of He–N₂O was found to deviate significantly from this model. The possible reason is discussed and the band-origin shift of Xe–N₂O predicted.     

Effects of ultrasound-assisted H2O2 on the solubilization and antioxidant activity of yeast β-glucan

Yeast β-glucan (YG) possess an extensive range of biological activities, such as the inhibition of oxidation, but the poor water solubility of macromolecular YG limits its application. In this study, through the combined degradation of ultrasonic waves and H₂O₂, and the optimization of the main process parameters for solubilizing YG by response surface methodology (RSM), a new product of YG_UH was generated. The molecular weight, structural characteristics and degradation kinetics before and after solubilization were evaluated. The results showed that the optimal solubilization conditions were reaction time: 4 h, ultrasonic power: 3 W/mL, H₂O₂ concentration: 24 %. Under these conditions, ultrasound-assisted H₂O₂ increased the solubility (from 13.60 % to 70.00 %) and reduced molecular weight (from 6.73 × 10⁶ Da to 1.22 × 10⁶ Da). Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Congo red (CR), scanning electron microscopy (SEM) revealed that ultrasound-assisted H₂O₂ increased the conformation's flexibility greatly, without changing the main structure of YG. More importantly, solubilization of YG improved free radical scavenging activity with YG_UH exhibiting the highest levels of DPPH and ABTS⁺ free radical scavenging activity. These results revealed that ultrasound-assisted H₂O₂ degradation could be a suitable way to increase the solubility of YG for producing value-added YG.     

Influence of iron ions on dielectric properties of the PbO–Bi2O3–B2O3 glass system

PbO–Bi₂O₃–B₂O₃ glasses containing small concentrations of Fe₂O₃ (0–1 mol%) were subject to dielectric studies (dielectric constant ε′; loss tan δ; and ac conductivity σ _ac) over a wide range of frequency and temperature. From spectroscopic (infrared, optical absorption and ESR spectra) and magnetic susceptibility studies, variations in these properties with dopant ion concentration were analyzed in terms of different oxidation states and iron ion environment in the glass network.