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1.
The transition from tin monoxide to tin dioxide is investigated by doping a low pressure premixed H2/O2/Ar flame with dilute concentrations of tetramethyl tin (TMT) Sn(CH3)4. The H2/O2 ratio was varied between 1.97 and 0.97; the reactor pressure was set to 30 mbar. The inlet gas velocity was kept constant and the precursor concentration was varied between 200 and 700 ppm. Mean particle diameters between 3 nm dp 7 nm were measured using a particle mass spectrometer (PMS), while X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis revealed information on crystal structure as well as morphology of the synthesized oxides. A gray SnO film was observed in the reactor at low oxygen concentrations, while for higher oxygen concentrations light yellow sub-stoichiometric tin oxides and white SnO2 were obtained. Further analysis of the sub-stoichiometric oxides, using atomic electron spectroscopy AES revealed that SnO2−x (0.2 x 0.6) was obtained. Furthermore, electrical characterization of all materials, deposited on interdigital capacitors, showed a decrease in the conductivity of the nanoparticles with increasing oxidation (decreasing x).  相似文献   

2.
Glass samples of composition xAl2O3-20PbO-(80−x)B2O3 and xWO3-xAl2O3-20PbO-(80−2x)B2O3 with x varying from 0% to 10% mole fraction are prepared by melt quench technique. The optical band gap decreases (from 3.21 to 2.37 eV) more for WO3-Al2O3-PbO-B2O3 glasses with an addition of WO3 content. The FTIR spectral studies have pointed out the conversion of structural units of BO3 to BO4 and WO4 to WO6 in these glasses. The increase in density from 4.51 to 5.80 g cm−3 for WO3-Al2O3-PbO-B2O3 glasses is observed with an increase in WO3 content. This is observed that the atomic structure changes more with the incorporation of WO3. This is due to the formation of WO6, WO4 and BO4 units.  相似文献   

3.
Glass samples of compositions 20PbO-80B2O3 and xWO3—(20−x) ZnO-20PbO-60B2O3 with x varying from 0% to 10% mole fraction are prepared by the melt quench technique. Decrease in the band gap from 2.86 to 2.16 eV for ZnO-PbO-B2O3 glasses with an increase in the WO3 content has been observed and discussed. The FTIR spectral studies have pointed out the conversion of structural units of BO3 to BO4 and WO4 to WO6 with the presence of W-O-W vibration of tungsten and incorporation of ZnO4 structural units of zinc in these glasses. The increase in density from 2.75 to 4.03 gcm−3 for ZnO-PbO-B2O3 glasses is observed with an increase in WO3 content. Due to the formation of WO6, WO4 and BO4 units, changes in the atomic structure with WO3 composition are observed and discussed.  相似文献   

4.
Commercial WO3 powder was annealed in air at four different temperatures and characterized by XRD and BET. The samples were used for the photooxidation of H2O to O2 under visible light irradiation (λ > 420 nm) in the presence of IO3 and the evolved gases were analyzed by gas chromatography. The results showed that the WO3 photocatalyst of monoclinic phase, which was obtained by annealing at 750 °C for 4 h, displayed the best activity in terms of O2 evolution among all the samples. Moreover, the activity was also found to be slightly affected by the grain size of the WO3 samples.  相似文献   

5.
α-Fe2O3-In2O3 mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1−x)Fe(NO3)3·9H2xIn(NO3)3·5H2O aqueous solution (x=0-1). X-ray diffraction and Mössbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the α-Fe2O3-In2O3 nanoparticle system together with the solubility limits of In3+ ions in the hematite lattice and of Fe3+ ions in the cubic In2O3 structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given.  相似文献   

6.
Glasses with composition xWO3·(30−x)M2O·70B2O3 (M=Li, Na; 0≤x≤15) doped with 2 mol% V2O5 have been prepared using the melt-quench technique. The electron paramagnetic resonance spectra have been recorded in X-band (ν≈9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) only due to V4+ ions, which exist as VO2+ ions in octahedral coordination with a tetragonal compression in the present glass system. The tetragonality increases with WO3:M2O ratio and also there is an expansion of 3dxy orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400-4000 cm−1 depicts the presence of WO6 group. The DC conductivity (σ) has been measured in the temperature range 423-623 K and is found to be predominantly ionic.  相似文献   

7.
Density functional theory (DFT) calculations are conducted to explore the interaction of H2 with pure and Ti-doped WO3 (002) surfaces. Four top adsorption models of H2 on pure and Ti-doped WO3 (002) surfaces are investigated respectively, they are adsorption on bridging oxygen O1c, absorption on plane oxygen O2c, absorption on 5-fold W5c (Ti), and absorption on 6-fold W6c. The most stable and H2 possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O2c site, while the favourable adsorption sites for H2 in a Ti-doped surface is not only an O2c site but also a W6c site. The adsorption energy, the Fermi energy level EF, and the electronic population are investigated and the H2-sensing mechanism of a pure-doped WO3 (002) surface is revealed theoretically: the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H2. It can be predicted that the method of Ti-doped into a WO3 thin film is an effective way to improve WO3 sensor sensitivity to H2 gas.  相似文献   

8.
The thermogalvanic power (Seebeck coefficient) of O2- conducting δ-Bi2O3 and δ-(Bi2O3)1−x(Y2O3)x has been measured directly as a function of temperature and partial oxygen pressure in N2---O2 mixtures. The of δ-(Bi2O3)0.75(R2O3)0.25 with R = Tb---Lu was indirectly determined using an isothermal concentration cell technique. Except for pure δ-Bi2O3, the heat of transport is much smaller than the activation energy for O2- conduction for all materials. The vibrational freedom of O2− ions in all δ-stabilized materials is reflected in their IR spectra at room temperature. Two prototypes of a thermogalvanic PO2 meter were tested.  相似文献   

9.
The red phosphors NaY1−xEux(WO4)2 with different concentrations of Eu3+ were synthesized via the combustion synthesis method. As a comparison, NaEu(WO4)2 was prepared by the solid-state reaction method. The phase composition and optical properties of as-synthesized samples were studied by X-ray powder diffraction and photoluminescence spectra. The results show that the red light emission intensity of the combustion synthesized samples under 394 nm excitation increases with increase in Eu3+ concentrations and calcination temperatures. Without Y ions doping, the emission spectra intensity of the NaEu(WO4)2 phosphor prepared by the combustion method fired at 900 °C is higher than that prepared by the solid-state reaction at 1100 °C. NaEu(WO4)2 phosphor synthesized by the combustion method at 1100 °C exhibits the strongest red emission under 394 nm excitation and appropriate CIE chromaticity coordinates (x=0.64, y=0.33) close to the NTSC standard value. Thus, its excellent luminescence properties make it a promising phosphor for near UV InGaN chip-based red-emitting LED application.  相似文献   

10.
Ga2O3 was-synthesized by doping a premixed H2/O2/Ar flat flame with diluted trimethyl gallium Ga(CH3)3 in a low-pressure reactor. The mean particle diameter d p of the resulting metal oxide was characterized in-situ with a particle mass spectrometer (PMS), and was observed to range between 2.5 nm ≤ d p ≤ 6.5 nm. XRD results show that the as-synthesized Ga2O3 nanoparticles are mostly amorphous, although, a few broad reflexes were observed that indicate the presence of some degree of crystallinity. Thermal annealing of the as-synthesized material at 1000 °C for 5 min yielded β-Ga2O3 with a monoclinic structure. UV–VIS measurements indicate strong absorption in the UV range (4.8 eV), which corresponds quite well to the direct band gap of bulk Ga2O3. Photoluminescence (PL) measurements of the as-synthesized metal oxide show a broad emission ranging from 350 nm to 600 nm with a maximum at 460 nm. Crystalline β-Ga2O3 exhibited stronger luminescence than as-synthesized particles.  相似文献   

11.
The combinatorial approach to materials synthesis was employed for the quick screening of a flux material for liquid phase-mediated epitaxy of Bi4Ti3O12 single crystal film. A series of ternary flux libraries composed of two self-fluxes (Bi2O3 and Bi4Ti3O12) and an impurity flux (VOx, WOx, CuOx, BiPOx, BaO, MoOx) were fabricated on the SrTiO3 (0 0 1) substrates. Then, stoichiometric Bi4Ti3O12 was grown on each one of these flux libraries at a temperature presumed to melt the flux. High-throughput characterization with the concurrent X-ray diffraction (XRD) method resulted in the discovery of a novel flux material, CuO, containing Bi2O3, for Bi4Ti3O12 single crystal film.  相似文献   

12.
CoFe2−xGdxO4 (x=0-0.25) nanoparticles were synthesized via a simple hydrothermal process at 200 °C for 16 h without the assistance of surfactant. The as-synthesized powders were characterized by X-ray diffraction, transmission electron microscopy, and a vibrating sample magnetometer. The X-ray diffraction results showed that the as-synthesized powders were in the pure phase with a doping amount of ≤0.25, and the peaks could be readily indexed to the cubic spinel cobalt ferrite. Transmission electron microscopy and high resolution transmission electron microscopy observations revealed that the gadolinium-doped cobalt ferrite nanoparticles were single crystal, roughly spherical, uniformly distributed, and not highly agglomerated. The room temperature magnetic field versus magnetization measurements confirmed a strong influence of gadolinium doping on the saturation magnetization and coercivity due to large lattice distortion and grain growth of small particles.  相似文献   

13.
Pure and WO3 doped CeO2-PbO-B2O3 glasses are prepared by the melt-quench technique. The structural and optical analyses of glasses are carried out by XRD, FTIR, density and UV-vis spectroscopic measurement techniques. FTIR analysis indicates the transformation of structural units of BO3 into BO4 with W-O-W vibration and the presence of WO4 and WO6 units observed with increase in WO3 contents. Decrease in band gap for CeO2-PbO-B2O3 glasses from 2.89 to 2.30 eV and for WO3 doped glasses from 2.89 to 1.95 eV has been observed and discussed. This decrease in band gap with WO3 doping approaches to semiconductor behavior. It shows that the presence of WO3 in the glass samples causes more compaction of the borate network due to the formation of BO4 groups and the presence of WO4 and WO6 groups, which result in a decrease in the optical band gap energy and increase in the density.  相似文献   

14.
WO3对掺铒碲酸盐玻璃光谱性质的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
制备了掺铒碲钨酸盐玻璃(80-x)TeO2-(10+x)WO3-8BaO-2Na2O-0.5Er2O3(x=0,5,10,15,20)玻璃,研究了WO3对掺铒碲钨酸盐玻璃的光谱性质. 研究发现:随着WO3含量的增加,Ω4,Ω6先增加后减小,受 关键词: 碲钨酸盐玻璃 3+光谱性质')" href="#">Er3+光谱性质 Judd-Offelt理论  相似文献   

15.
RuSex electrocatalytic nanoparticles were deposited onto hybrid carriers composed of Black Pearl carbon-supported tungsten oxide; and the resulting system's electrochemical activity was investigated during oxygen reduction reaction. The tungsten oxide-utilizing and RuSex nanoparticle-containing materials were characterized using transmission electron microscopy, X-ray diffraction and electrochemical diagnostic techniques such as cyclic voltammetry and rotating ring-disk voltammetry. Application of Black Pearl carbon carriers modified with ultra-thin films of WO3 as matrices (supports) for RuSex catalytic centers results during electroreduction of oxygen in 0.5 mol dm−3 H2SO4 (under rotating disk voltammetric conditions) in the potential shift of ca. 70 mV towards more positive values relative to the behavior of the analogous WO3-free system. Also the percent formation (at ring in the rotating ring-disk voltammetry) of the undesirable hydrogen peroxide has been decreased approximately twice by utilizing WO3-modified carbon carriers. The results are consistent with the bifunctional mechanism in which oxygen reduction is initiated at RuSex centers and the hydrogen peroxide intermediate is reductively decomposed at reactive WO3-modified Black Pearl supports. The electrocatalytic activity of the system utilizing WO3-modified Black Pearl supports has been basically unchanged upon addition of acetic acid, formic acid or methyl formate to the sulfuric acid supporting electrolyte.  相似文献   

16.
Garnet nanoparticles Y3−xSmxFe5O12 were fabricated by a sol–gel method. The XRD patterns of all the samples have only peaks of the garnet structure and the sizes range from 34 to 67 nm. Results of VSM show that the saturation magnetization of Y3−xSmxFe5O12 (0<x3) decreases on increasing the Sm concentration x evidently. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.  相似文献   

17.
Intense red phosphors, AgGd1−xEux(W1−yMoy)2O8 (x=0.0-1.0, y=0.0-1.0), have been synthesized through traditional solid-state reaction and characterized by X-ray diffraction (XRD) and photoluminescence (PL). XRD results reveal that AgGd1−xEuxW2O8 synthesized at 1000 °C has a tetragonal crystal structure, which is named as high temperature phase (HTP) AgGdW2O8. All phosphors compositions with Eu3+ show red and green emission on excitation either in the charge-transfer or Eu3+ levels. Analysis of the emission spectra with different Eu3+ concentrations reveal that the optimum dopant concentration for Eu3+ is x=0.6 in the HTP AgGd1−xEuxW2O8 (x=0.0-1.0). Studies on the AgGd0.4Eu0.6(W1−yMoy)2O8 (y=0.0-1.0) and AgGd1−xEux(W0.7Mo0.3)2O8 (x=0.0-1.0) show that the emission intensity is maximum for compositions with y=0.3 and x=0.5, respectively, and a decrease in emission intensity is observed for higher y or x values. The Mo6+ and Eu3+ co-doped AgGd(WO4)2 phosphors show higher emission intensity in comparison with the singly Eu3+-doped AgGd(WO4)2 in UV region. The intense emission of the tungstate/molybdate phosphors under 394 and 465 nm excitations, respectively, suggests that these materials are promising candidates as red-emitting phosphors for near-UV/blue GaN-based white LED for white light generation.  相似文献   

18.
Ni1−xCoxFe2O4 (x=0.6, 0.8 and 0.9) nanoparticles have been synthesized with various crystallite sizes depending on the thermal treatments and composition (cobalt content) using the sol-gel combustion method. The size of nanoparticles has been controlled by thermal treatment. On the other hand, the magnetic property of the ferrite has been controlled by changing the heat treatment. Morphology and particle sizes of Ni1−xCoxFe2O4 have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The presence of functional group has been identified by Fourier Transform Infrared (FTIR) spectra. From TGA-DTA studies, the weight gains of Ni1−xCoxFe2O4 nanoparticles have been observed and it might be due to capping organic molecules with oxygen at temperatures above 200 °C. Magnetic properties of Ni1−xCoxFe2O4 particles have been analysed using VSM and it is found that saturation magnetization (Ms) has increased with particle size and has coercivity (Hc) increased initially and then decreased. The Ms and Hc values decreased with the increase of content of cobalt in Ni1−xCoxFe2O4.  相似文献   

19.
The redox reaction of Ce4+-Ce3+ promoted by the catalytic function of nickel ions in a (1−x)CeO2-xNiO solid solution was investigated for solar H2 production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O2-releasing reaction with (1−x)CeO2-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H2 gas evolved by the reduced form were 1.2-2.5 cm3/g and the evolved gases amounts ratio of H2/O2 was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H2O=H2+1/2O2). The maximum amounts of evolved H2 and O2 gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO2-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O2-releasing and H2-generation reactions with (1−x)CeO2-xNiO solid solution were repeatable with the redox system of Ce4+-Ce3+, which was enhanced by the catalytic function of Ni2+-Ni0.  相似文献   

20.
SnO2/TiO2 mixed oxides with primary particle size ranging between 5 nm dp 12 nm were synthesized by doping a H2/O2/Ar flame with Sn(CH3)4 and Ti(OC3H7)4 co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO2 and SnO2, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.  相似文献   

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