Relaxation studies on V2O5-TeO2 glasses using heterogeneous conductor model

The dielectric modulus spectra of glasses in the system V₂O₅-TeO₂ have been studied as a function of frequency in the temperature range 230 to 330K. A heterogeneous conductor model developed recently with the assumption of a sinusoidally varying local conductivity in the conducting phase has been successfully applied to analyse the data in this glass system. The Kohlrausch-Williams-Watts (KWW) stretched exponential function has also been used to fit the measured modulus spectra. The exponentβ is found to be correlated to the conductivity fluctuation in the conducting phase as assumed in the heterogeneous model.     

Conversion of V2O5·xH2O into orthorhombic V2O5 single-crystalline nanobelts

Orthorhombic V₂O₅ single-crystalline nanobelts have been synthesized by hydrothermal treating V₂O₅·xH₂O precipitate derived from aqueous solution of V₂O₅ and H₂O₂. The synthetic method is facile, fast, environmental friendly, and easy to scale up. The V₂O₅ single-crystalline nanobelts are 30-80 nm in width, 30-40 nm in thickness, and lengths up to several tens of micrometers. The V₂O₅·xH₂O precursor is crucial for the formation of orthorhombic V₂O₅ single-crystalline nanobelts. The influences of synthetic parameters, such as reaction time and reaction temperature, on the crystal structures and morphologies of the resulting products have been investigated. Time-dependent experiments show that V₂O₅·xH₂O are dehydrated gradually and converted into orthorhombic V₂O₅ single-crystalline nanobelts. High reaction temperature also favors the formation of orthorhombic V₂O₅ nanobelts.     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

High temperature resistivity characteristics of nonstoichiometric V2O3

The resistivity anomaly encountered in stoichiometric V₂O₃ is gradually suppressed with increasing density of cation vacancies. These observations are discussed in terms of related findings reported in the literature. Research supported by NSF-MRL Grant DMR 77-23798.     

Growth of carbon nanotubes over Fe-Co and Ni-Co catalysts supported on different phases of TiO2 substrate by thermal CVD

The aim of this work is to examine the properties of CNTs formed on Fe-Co and Ni-Co bimetallic catalysts supported on different phases of TiO₂ (anatase and rutile) by wet impregnation method. The CNTs are grown from decomposition of acetylene via Thermal CVD at 700°C using the prepared catalysts. The nanomaterials were characterized by XRD, Xmap, BET, FESEM, TEM, and Raman spectroscopy. It was found that the catalyst samples supported on rutile TiO₂ have higher specific surface area, smaller catalytic nanoparticles with denser distribution and very more activity compared to anatase ones. Consequently, the CNTs nucleated from nanoparticles supported on rutile TiO₂ possess higher density, smaller average diameters and narrower diameter distribution compared to grown CNTs on anatase samples. Moreover, it was observed that the Fe-Co bimetallic catalysts regardless of TiO₂ support phase, possesses more catalytic activity and higher average growth rate of CNTs in compare with Ni-Co catalysts.     

等离子体电解氧化法制备多孔TiO2/V2O5复合物膜层及其增强光催化产氢活性

较差的光催化产氢效率极大地阻碍了TiO₂光催化剂的工业化应用。为此,本文在含有NH₄VO₃的磷酸盐溶液中,采用等离子体电解氧化(PEO)法制备了多孔TiO₂/V₂O₅复合膜光催化剂,通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、X射线光电子谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)对其组成、结构及光吸收性质进行了表征,并采用气相色谱评价了薄膜催化剂的光催化产氢性能,研究了电解液中NH₄VO₃含量对膜的结构、组成和光催化产氢性能的影响。结果表明:复合膜催化剂主要由锐钛矿和金红石型TiO₂组成,具有微孔结构,V₂O₅主要以无定形形式存在于膜中,与TiO₂有很强的相互作用,影响TiO₂的晶面间距。研究发现,元素V抑制了TiO₂的结晶和金红石型TiO₂的形成,扩大了薄膜的光学吸收范围。针对Na₂S+ Na₂SO₃溶液中的光催化产氢性能的研究显示,在质量浓度为1 g/L NH₄VO₃的电解液中制备的TiO₂/V₂O₅薄膜的光催化活性最高,优于近年来报道的其他光催化剂。光催化重复实验表明,该复合膜催化剂具有较高的稳定性和较为恒定的光催化活性。     

Thermo-optic properties of TiO2, Ta2O5 and Al2O3 thin films for integrated optics on silicon

The direct measurement of the thermo-optic coefficients of aluminium oxide, tantalum pentoxide and titanium dioxide thin films is presented. Using ellipsometry on monolithically integrated permutations of the layers of silicon, silicon dioxide and the material under test, allows the direct measurement of the overall thermo-optic coefficient accounting for thermally induced changes in the dielectric permittivity and density of the materials as well as the elasto-optic effect due to the non-matching thermal expansion coefficients of the different materials.     

High-performance Cu-doped vanadium oxide (CuxV2O5) prepared by rapid precipitation method for rechargeable batteries

Cu_xV₂O₅ (x = 0, 0.15, 0.25) was prepared by acidifying aqueous NaVO₃ with diluted H₂SO₄ followed by mixing Cu powder with V₂O₅ precipitate. The method is a rapid synthesis procedure, compared to the ion-exchange method. The effect of copper on the characteristics of V₂O₅ was also investigated. These materials maintained the layered structure typical of V₂O₅ xerogel. It was found that the copper-doped V₂O₅ material exhibits better cycle performance than the undoped V₂O₅. Cu_0.25V₂O₅ showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5-4.0 V at 96 mA/g (C/3). After the 100 consecutive cycles, the specific capacity of the Cu_0.25V₂O₅ electrode maintained 219.5 mA h/g. The doped material prepared by the rapid method shows better a cycling performance, compared to the ion-exchange method.     

Synthesis and characterization of core-shell nanostructured PPy/V2O5 composite

Polypyrrole/V₂O₅ (PPy/V₂O₅) composite was synthesized successfully by in-suit chemical oxidation polymerization of pyrrole in the host of inorganic matrix, using complex of methyl orange (MO)/FeCl₃ as a reactive self-degraded soft-template. The morphology and molecular structure of the composite were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) transmission spectra, X-ray diffraction analysis (XRD) and thermogravimetric analysis (TGA). The results indicated that PPy/V₂O₅ composite possessed the typical core-shell nanostructures, in which the irregularly shaped V₂O₅ particles act as the “core”, while the self-assembled PPy nanotubes serve as the “shell” of the composite. And there was no obvious chemical interaction but some physical interaction between PPy and V₂O₅ in the composite.     

NH4Zr2V3O12 proton conductor

NH₄Zr₂V₃O₁₂, a new proton conductor, has been synthesized by flux, melt and hydrothermal methods. The crystals were subjected to X-ray diffraction, differential thermal analysis, infrared spectroscopy and impedance measurements.     

Morphology characterization and friction coefficient determination of sputtered V2O5 films

The morphology of V₂O₅ low-friction coatings on MgO (001) substrates synthesized by unbalanced reactive magnetron sputtering was investigated using atomic force microscopy. Analyzing the height-height correlation function, the evolution of the surface roughness parameters root mean square roughness (rms), lateral correlation length, and the Hurst parameter were determined. Studying samples of V₂O₅ grown at temperatures from 25 °C to 300 °C, a transition from amorphous to crystalline growth at 80 °C was observed. The rms roughness increased from 0.7 nm at 26 °C to 21 nm at 300 °C. Furthermore, a method to quantitatively determine friction coefficients via friction force microscopy was applied. The surface contact forces were calculated via the cantilever's spring constants determined using the Sader method. At scan speeds of 1.25 μm/s and 3.13 μm/s, friction coefficients of 0.60 ± 0.02 and 0.63 ± 0.01, respectively, have been obtained.     

堇青石改性V2O5-WO3/TiO2催化剂性能影响研究

采用固液混合方法,利用改性堇青石制备蜂窝式V2O5-WO3/Cordierite-TiO2脱硝催化剂,通过扫描电子显微镜(SEM)、热分析(DSC-TG)、X射线衍射分析仪(XRD)、模拟烟气分析装置和磨损装置,考察其表面形貌、热稳定性、晶相变化、耐磨损性能和催化剂活性。结果表明,改性堇青石的引入,制备的催化剂具有表面微气孔多和热稳定性好的特点,700℃煅烧后,V2O5和WO3的仍呈现无定形态或微晶状态;引入10%的堇青石制备的催化剂磨损率低,尤其在250～460℃反应时,脱硝率可以保持在80%以上。     

Growth and structure of electron beam evaporated V2O5 thin films

The growth, structure and room temperature electrical conductivity of electron beam evaporated V₂O₅ thin films were studied in detail as a function of deposition temperature. The films deposited at T_s≈553 K and subsequently annealed in oxygen atmosphere at 693 K exhibited orthorhombic layered structure.     

Preparation and characterization of Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film as electrode material for the degradation of phenol

In this work, a novel electrode of titanium substrate coated with mixed metal oxides of SnO(2), Sb(2)O(3), Nb(2)O(5) and PbO(2) was successfully prepared using thermal decomposition and electrodeposition. The surface morphology and the structure of the prepared thin film were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. Experimental results showed that the structure of the prepared electrode might be described as a Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film and its surface was mainly comprised pyramidal-shape beta-PbO(2) crystals. The modified electrode had higher oxygen evolution potential than that of other PbO(2) modified electrodes. Electrocatalytic oxidation of phenol in aqueous solution was studied to evaluate the potential applications of this electrode in environmental science. The phenol removal efficiency in an artificial wastewater containing 0.50g/L phenol could reach 78.6% at 20 degrees C and pH 7.0 with an applied electricity density of 20mA/cm(2) and treatment time of 120min. When 21.3g/L chloride was added to this wastewater, the removal efficiency could reach to 97.2%.     

Gravitational waves detector mirrors: Spectroscopic ellipsometry study of Ta2O5 films on SiO2 substrates

A stack of Ta₂O₅/SiO₂ layers is presently used as coating layer of mirrors in interferometric detectors for gravitational waves. The sensitivity of these detectors is limited in the 50-300 Hz frequency range by the mirror thermal noise, and it was suggested that mechanical losses in the Ta₂O₅ are the dominant source of noise. We focus here on Spectroscopic Ellipsometry (SE) results (in the 0.75 ÷ 5 eV spectral range) obtained on high quality Ta₂O₅ films deposited on SiO₂ substrates by Double Ion Beam Sputtering at the Laboratoire des Matériaux Avancés (Lyon, France). The films are extremely flat as indicated by the 0.2 nm RMS roughness determined by Atomic Force Microscopy (AFM) on (20 × 20) μm² areas. The comparison of the optical properties determined by SE with literature data, corroborated by X-ray Photoelectron Spectroscopy (XPS) data, suggests that the films present a non-ideal bulk stoichiometry and/or some degree of nanoporosity. The possible influence of an interface layer is also discussed.     

Electronic and Magnetic Properties of Superconducting Sr4V2Fe2As2O6 Versus Sr4Sc2Fe2As2O6

First principles of FLAPW-GGA calculations have been performed with the purpose to understand the peculiarities of band structure and Fermi surface topology for recently discovered 37 K superconductor: Sr₄V₂Fe₂As₂O₆—in comparison with isostructural phase Sr₄Sc₂Fe₂As₂O₆. Our main finding is that the replacement of Sc with V leads to drastic transformation of electronic, magnetic and conductive properties of these materials: as against non-magnetic Sr₄Sc₂Fe₂As₂O₆ which is formed from non-magnetic conducting [Fe₂As₂] and insulating [Sr₄Sc₂O₆] blocks, Sr₄V₂Fe₂As₂O₆ consists of non-magnetic conducting [Fe₂As₂] blocks and [Sr₄V₂O₆] blocks which exhibit magnetic half-metallic properties.     

Synthesis and photocatalytic property of SnO2/TiO2 nanotubes composites

SnO2/TiO2 nanotubes composite photocatalysts with different SnO2 contents were successfully synthesized by means of a simple solvothermal process. The synthesized products were characterized physically by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The composite photocatalysts can not only make the target pollutant, methylene blue (MB), adsorbed at a high concentration level around the surface of the composites but also decrease the recombination rate of electron-hole pairs so as to achieve good photocatalytic performance. The effect of SnO2 contents on the photocatalytic activities of the composites was also investigated. The results showed that the SnO2/TiO2 nanotubes composite photocatalyst with 5 wt.% SnO2 loading had the highest photocatalytic efficiency.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

Preparation and photocatalytic activity of novel efficient photocatalyst Sr2Bi2O5

A novel visible-light-driven photocatalyst of Sr₂Bi₂O₅ is prepared by solid-state reaction at 780 °C. The optical band gap of Sr₂Bi₂O₅ is determined to be 2.87 eV by UV-Vis diffuse reflectance spectroscopy. Under both UV and visible-light irradiation, the photocatalytic activity for degrading methyl orange (MO) over Sr₂Bi₂O₅ is higher than those over BiVO₄, and SrBi₂O₄. The relationships between the photocatalytic properties of Sr₂Bi₂O₅, SrBi₂O₄, and BiVO₄ and their crystal structures are discussed. Among Sr₂Bi₂O₅, SrBi₂O₄, and BiVO₄, the higher photocatalytic activity of Sr₂Bi₂O₅ is ascribed to its higher level of distortion of the metal-oxygen polyhedra, and the lower packing factor degree.     

Synthesis of Nb2O5 nanosheets and its electrochemical measurements

In this study, Nb₂O₅ nanosheets were first synthesized using NbO₂ particles as the precursor via a simple hydrothermal route. The synthesized Nb₂O₅ nanosheets are highly crystalline and their thicknesses are found to be ca. 3–5 nm. Based on the experimental results of XRD, SEM and TEM measurements, a possible mechanism for the formation of nanosheets was discussed. An electrode materials made of the product containing Nb₂O₅ nanosheets shows a larger capacity of 355 mAh g⁻¹ at a current density of 0.1 A g⁻¹. Cyclic measurements indicate that such an electrode exhibits a high reversible charge/discharge capacity and cycling stability. This might be attributed to the intrinsic characteristics of Nb₂O₅ nanosheets.