Increase In MoO Research Articles

Tailored structure and photoluminescence of substoichiometric molybdenum oxide nanomaterials by doping of gallium oxide

Substoichiometric molybdenum oxide (MoO 3- x ) nanomaterials become the promising structure-dependent semiconductor materials. However, the structural tuning of MoO 3- x nanomaterials is still an important challenge. Here we report the tuned MoO 3- x nanostructures via the doping of Ga 2 O 3 in hot filament chemical vapor deposition system. The diverse characterization results indicate that the addition of Ga 2 O 3 in the MoO 3 precursor leads to the doping of Ga 2 O 3 in the MoO 3- x nanostructures and the increase of the MoO 2 component in MoO 3- x nanomaterials. Furthermore, the addition of Ga 2 O 3 improves the regularity of MoO 3- x nanoparticles (NPs) and induces the lattice expansion of MoO 3- x nanostructures. The photoluminescence (PL) properties were measured at room temperature. The PL results exhibit that the synthesized MoO 3- x nanomaterials generate the ultraviolet, blue, green, red and near infrared light due to the bandgap transition, the transition between two sub-bands, the intervalence charge transfer transition and the transition from the intermediate level to valence band, respectively. In addition, the PL results also reveal the PL quenching due to the doping of Ga 2 O 3 , which is related to the reduction of nanocavities, the aggregation of the MoO 3- x NPs and the increase of MoO 2 phase induced by the incorporation of Ga 2 O 3 in the MoO 3- x nanostructures. These achievements can contribute to the tuning of MoO 3 -based nanostructures and the development of next-generation optoelectronic nanodevices based on doping-engineered MoO 3 nanomaterials. • MoO 3- x nanomaterials with a low doping level of Ga 2 O 3 . • Tailored structures of MoO 3- x nanomaterials by doping of Ga 2 O 3 . • Tunable optical properties of Ga 2 O 3 -doped MoO 3- x nanomaterials.

Structure and dielectric constant of silver molybdophosphate mixed network former glasses

Structure and dielectric constant of silver molybdophosphate mixed network former glasses have been reported in this paper. The Fourier transform infrared (FTIR) spectroscopy has been used to investigate the effect of MoO 3 on the glass network structure. The existence of characteristic absorption bands corresponding to the vibration of P O bond, P–O − mode and P–O–P bond and the presence of MoO 4 2− anions have been ascertained from the FTIR spectra. It is observed that the increase of MoO 3 content in the compositions changes the network structure by creating non-bridging oxygen caused by the breaking of long phosphate chains. It is further observed that the dielectric constant and dielectric strength of these glasses increases with the increase of MoO 3 content, which is attributed to the increase of the polarizability of the glasses due to addition of MoO 3.

Production and properties of high purity TeO 2–ZnO–Na 2O–Bi 2O 3 and TeO 2–WO 3–La 2O 3–MoO 3 glasses

High-purity TeO 2–ZnO–Na 2O–Bi 2O 3 and TeO 2–WO 3–La 2O 3–MoO 3 glasses were produced by melting the high-purity oxides mixtures in platinum or gold crucible at 800 °C in hermetic chamber in the purified oxygen atmosphere. The content of limiting impurities in the produced initial oxides and glasses, the optical properties as well as the stability to crystallization were investigated. The optical fibers were produced from high-purity tellurite glasses with losses at the level of several hundreds of dB/km. The total content of 3d-transition metals in the glasses was not more than 1 ppm wt and content of hydroxyl groups corresponded to the absorption level of 0.001–0.002 cm −1 at ∼3 μm. The absorption band, monotonically increasing with the increase in MoO 3 content, was observed in dry TeO 2–WO 3–La 2O 3–MoO 3 glasses with the maximum at about 3.7 μm.

Effect of molybdenum tri-oxide molar ratio on the optical and some physical properties of tellurite–vanadate–molybdate glasses

Glasses with composition (60 − x)V 2O 5–40TeO 2 − x MoO 3 with 20 ⩽ x ⩽ 60 (in mol%) have been prepared using the usual melt quenching method. The optical absorption spectra of the glasses have been recorded in the wavelength range 300–800 nm. The position of the absorption edge and therefore the optical band gap values were found to be depend on the glass composition. For these glasses, the optical band gap was found to be in the range 2.03–2.86 eV with increasing of MoO 3 concentration. The absorption spectrum fitting method was employed to obtain the energy gap. In this method, only the measurement of the absorbance spectrum of the glass is needed. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in MoO 3 concentration as a network former.

Influence of MoO 3 doping on structure and electrical conductivity of defect fluorite-type Gd 2Zr 2O 7

In this paper, we report the preparation, structure and electrical conductivity of MoO 3-doped zirconates with a nominal chemical formula of Gd 2(Zr 1− x Mo x ) 2O 7+2 x ( x = 0, 0.1, 0.2). X-ray diffraction measurements indicate that Gd 2Zr 2O 7 exhibits a defect fluorite-type structure, and Gd 2(Zr 1− x Mo x ) 2O 7+2 x ( x = 0.1, 0.2) have a single phase of pyrochlore-type structure. The alternating current (AC) impedance measurements show that the electrical conductivity of Gd 2(Zr 1− x Nb x ) 2O 7+2 x ceramics obeys the Arrhenius equation, and gradually increases with increasing temperature from 673 to 1173 K. The activation energy and pre-exponential factor for electrical conductivity gradually decrease with the increase of MoO 3 content. Gd 2(Zr 1− x Mo x ) 2O 7+2 x ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10 −4 to 1.0 atm at all test temperature levels. The electrical conductivity of defect fluorite-type Gd 2Zr 2O 7 is not improved by MoO 3 doping.

1.4μm emission properties and local environments of Tm3+ ions in tellurite glass modified with MoO3

Abstract The 1.4 μm emission properties of Tm 3+ ions embedded in tellurite glass containing MoO 3 have been investigated in an effort to develop non-crystalline materials for ultra broadband optical amplifier. Spectral lineshape and bandwidth of the 1.4 μm emission exhibited a negligible dependence on amount of MoO 3 , while the measured lifetime of the Tm 3+ : 3 H 4 state decreased with increase in MoO 3 content. Multiphonon relaxation turned out to become stronger with increase in MoO 3 amount, which coincided with the further broadened Raman scattering bandwidth of the MoO 3 -containing tellurite glass. The spectroscopic properties of Tm 3+ ions doped in our modified tellurite glasses are discussed in connection with the local structural parameters obtained from Tm L 3 -edge EXAFS analysis.

Role of molybdenum ions on physical, optical, electrical and vibrational studies in Er 3+ co-doped TeO 2–ZrO 2–PbCl 2 glasses

(75 − x)TeO 2–15PbCl 2– xMoO 3–10ZrO 2 doped with 5 mol% Er 2O 3, where x = 2.5, 5, 7.5 and 10 mol%, glasses were investigated by Raman spectroscopy, dc conductivity, optical transmittance spectra and density were measured. Mo O bonds are present in the entire glass composition. The glasses contain TeO 4 trigonal bipyramids, TeO 3+1 polyhedra and MoO 6 octahedra as basic structural units. Glasses having low MoO 3 content contain MoO 6 octahedra having two Mo O bonds. As MoO 3 content increases, the fraction of Mo O bonds to Mo 6+ decreases. The dc conductivity increases with increase in MoO 3 content, and the activation energy decreases with increase in MoO 3 content. The optical band gap ( E opt ) and Urbach energy ( E r ) were determined from the optical transmittance spectra of the polished samples recorded in the spectral range from 190 to 1100 nm at room temperature (RT). Variation in these optical parameters has also been associated with the structural changes occurring in these glasses with increase in MoO 3 content, and the present glasses behave as indirect gap semiconductors.

Effects of MoO 3 and TiO 2 additions on the magnetic properties of manganese–zinc power ferrites

The effects of MoO 3 and TiO 2 additions on the magnetic properties of manganese–zinc (MnZn) power ferrites are investigated. It is found that the power loss P v and the initial permeability μ i of MnZn power ferrites are found to fluctuate with the increase of MoO 3 content, and the magnetic properties can be considerably improved with suitable amount of MoO 3 addition. At 100 °C, compared to the reference sample without MoO 3 addition, the sample doped with 600 ppm MoO 3 has a decrease of 13.5% in P v to 451 mW/cm 3, and an increase of 7.2% in μ i to 3973 mW/cm 3. Besides, proper doping of TiO 2 can further improve the magnetic properties of MnZn power ferrites. The sample doped with 400 ppm TiO 2 demonstrates a decrease of 5.78% in P v at 100 °C, and a reduction of 25% in the thermal coefficient for 80–120 °C. The mechanisms of the above improvements by doping MoO 3 and TiO 2 are briefly analyzed.

Structural characterization and catalytic activity of molybdenum oxide supported zirconia catalysts

A series of MoO 3/ZrO 2 catalysts with different molybdenum content of 5–30 wt.% MoO 3 were prepared by impregnation method. The prepared catalysts were calcined at 400, 550, 700, 800, and 1000 °C. The structural characteristics were investigated by means of thermal analysis (DTA and TGA), powder X-ray diffraction (XRD) while the textural properties was determined from low temperatures adsorption of N 2 at −196 °C. The surface acidity was measured with nonaqueous titration of n-butylamine in acetonitrile. The catalytic activity was tested by cumene dealkylation and ethanol conversion using the microcatalytic pulse technique. XRD reveals that the samples contain mixture of tetragonal and monoclinic zirconia phases. At low MoO 3 loading, i.e. <15 wt.% MoO 3, MoO 3 was not detected. When the loading of MoO 3 exceeds 15 wt.%, crystalline MoO 3 and Zr(MoO 4) 2 were formed, particularly for the higher calcination temperature products. The incorporation of MoO 3 into ZrO 2 enhanced the surface acidity of the catalysts. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 400 to 550 °C and also with the molybdenum oxide content. This increase in the surface acidity was correlated with the degrees of crystallinity of the samples. The surface area was found to increase with increasing of MoO 3 up to 15 wt.%. Further increase of MoO 3 beyond 15 wt.% led to a decrease of N 2- S BET. The catalytic activity was strongly influenced with the textural, structural properties and surface acidities of the catalysts investigated.

Structure and catalytic properties of molybdenum oxide catalysts supported on zirconia

MoO 3/ZrO 2 catalysts with different MoO 3 loadings (2–12 wt%) were prepared by the wet impregnation method. These catalysts were characterized by various techniques, such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of NH 3 and the catalytic properties were evaluated for vapor-phase ammoxidation of toluene to benzonitrile. XRD patterns show the presence of crystalline MoO 3 peaks above 6.6 wt% MoO 3, which corresponds to the theoretical monolayer loading of MoO 3 on the zirconia used in the present study. The TPR suggests that reduction of the catalysts occurs in two stages and indicates that the reducibility of the catalysts increases with increase in MoO 3 loading up to 6.6 wt%. The acidity of the catalysts was also found to increase up to 6.6 wt% of molybdena loading and it does not increase much at higher loadings. Raman results show that the surface molybdate species are present in low-loading samples, while crystalline MoO 3 bands are observed from 9 wt% of MoO 3 and above loadings. XPS spectra showed that molybdenum was present at Mo 6− on all fresh samples. The Mo/Zr atomic ratio shows that the dispersion of molybdena is high below 6.6 wt% MoO 3 and dispersion decreases at higher molybdena loadings. The catalytic activity of the catalysts during ammoxidation of toluene was found to increase with loading up to 6.6 wt% and did not change appreciably beyond this loading.

Effect of mixed glass-formers in Ag 2O.MoO 3.TeO 2 system

A comprehensive study of the partial replacement of tellurium by molybdenum in Ag 2O.TeO 2 binary glass system resulting in yAg 2 O.(1 − y[ xMoO 3.(1 − x) TeO 2] ternary system has been carried out through X-ray diffraction, differential scanning calorimetry, electrical conductivity, X-ray photoelectron spectroscopy and infrared spectroscopy measurements. The observed variations in the glass transition temperature with change in composition were correlated to the bond strength, cross-link density and closeness of packing in the glass network. The conductivity measured at 25 °C shows two maxima for y = 0.30 at x = 0.2 and 0.4 and for y = 0.40 at x = 0.3 and 0.5. The enhancement of conductivity with an increase in MoO 3 content is about half an order of magnitude. The observed changes in conductivity were attributed to the structural modifications resulting in the creation of nonbridging oxygen atoms which were distinguished from the bridging oxygen atoms through the deconvoluted O 1s XPS spectra. The deconvoluted Te 3d XPS spectra were assigned to various tellurium based structural units.

Preparation of cuprous ion-conducting glasses in the system CuICu 2OMoO 3

The glass formation was tried in the systems CuICu 2OM m O n , where M m O n is B 2O 3, V 2O 5, MoO 3 or WO 3. The glasses, however, were only obtained in the CuICu 2OMoO 3 system. The glass-forming region was mainly found in pseudobinary system CuICu 2MoO 4, similar to glasses in the system AgIAg 2OMoO 3. Glass transition temperatures range from 125 to 150°C and do not change so much with CuI content while they increase with an increase in MoO 3 content. The IR spectra showed that the pseudobinary glasses were only composed of Cu +, I − and monomer MoO 4 2− ions, and classified as “ionic” glasses containing one type of cations. The molar volume of the glasses in the pseudobinary system was primarily determined by a fairly dense packing of the constituent anions, I − and MoO 4 2−.

Some physico-chemical properties of Molybdenum Oxide supported on γ-Alumina

The oxidised and reduced states of MoO 3Al 2O 3 catalysts containing up to 30 wt.% MoO 3 have been studied by various chemical-physical techniques. The system can roughly be divided into two main regions centered around 15 wt.% MoO 3 on the basis of the nature of the surface structures which are governed by the molybdenum concentration and the acidity of the support. Generally, increase of MoO 3 leads from monolayer to multilayer deposition, and correspondingly from tetrahedral monomeric to octahedral polymeric species. In particular, oxyanionic species of the type [MoO 4] 2− in oxidised, and [MoO 4] 3− in reduced samples were detected in the low (< 4 wt.%) molybdenum content catalysts. In the intermediate range, polyoxyanionic forms (dimolybdates) are found in oxidised samples; in reduced catalysts both oxyanionic forms (reduced molybdates and dimolybdates) and oxycationic mono- and bis-molybdenyl species are present. In MoO 3-rich oxidised catalysts (> 15 wt.% MoO 3) oxyanionic species are found as polymolybdates, as well as the oxycationic form [MoO 2] 2+; also part of the molybdenum is incorporated in the octahedral vacancies of the support and Al 2(MoO 4) 3 is formed. Reduced samples give evidence for structures containing Mo(VI) and Mo(V) (reduced heteropolyacids) and the oxycationic species MoO 3+ at the most acidic sites, both at the surface and in the bulk. The effect of increasing temperature is that the species described are present at lower concentration threshold limits.