MoO3 Crystals Research Articles

On the Reduction of Orthorhombic MoO3 to MoO2

Electron diffraction shows evidence of topotactic orientation relationships between the original MoO3 crystal and MoO2 crystals formed under mild reduction conditions. These relationships differ from previously published literature data. A possible mechanism of formation of the [100] strings of edge sharing octahedra in the MoO2 structure is tentatively proposed.

Formation of double oxides by coalescence of smoke particles of different oxides

Particles in a mixture of a MoO3 smoke and a Bi2O3 smoke were investigated by electron microscopy and X-ray microanalysis. They were crystals of MoO3, Bi2O3, Bi2 (MoO4)3, Bi2MoO6, and peritectic mixtures of these oxides. The double oxides could be produced in the smokes mixed at location where no oxide vapor existed. The formation of these double oxides thus is regarded as a corroborative evidence of the coalescence of the metallic oxide particles. It was also found that coalescence between MoO3 and Bi2O3 particles took place above 350°C in a short time of ∽ 10−2 s.

White and Black Strap Contrast Observed in the X-Ray Magnified Laue Images of MoO3 Crystals

White and black strap contrasts appearing in Magnified Laue diffraction images of molyb-denum trioxide single crystals which had been prepared by the vapour transport method were analysed experimentally by using an X-ray and an electron microscope. The white part of the strap contrast appeared due to the amorphous structure which formed from the liquid phase of the materials at the steps accompanied by crystal growth. The black fringe parts of the contrast appeared due to the distorted regions which were produced in the matrix at the regions adjacent to the amorphous structure.

Long-range potential centres in disordered solids

Measurements are reported on the AC and DC conductivity of evaporated films and single crystals of MoO3. In both cases a frequency-dependent conductivity is observed at low temperatures, and it is established that this is a true bulk property. A model is developed which shows that long-range potential wells surrounding centres such as (O2-) vacancies play a substantial role in the transport process. In particular, DC conduction requires movement of carriers between such wells, while AC conduction can occur within a single well. The resulting difference in the distribution of relaxation times and hopping distances involved can account for inconsistencies between parameters deduced from DC, AC and high-field transport measurements. An improved method is proposed for the calculation of the density of states involved in hopping transport.

ESR- and magnetic susceptibility measurements on the potassium molybdenum bronzes

Magnetic and transport properties of the transition metal bronzes are determined by the extent of delocalization of the transition metal 4d-electrons. We report on ESR investigations of single crystals of the “red” potassium molybdenum bronze K0.33MoO3 and of the “blue” potassium molybdenum bronze K0.30MoO3. ESR spectra due to unpairedd-electrons are observed at both compounds. Analyzing the hyperfine structure we find that thed1-electrons are delocalized over six molybdenum lattice sites in semiconducting K0.33MoO3. The same K0.33MoO3 crystals show another spectrum which is caused by pairs of exchange coupledd-electrons. Our results are compared with those from magnetic susceptibility measurements and are discussed in connection with the crystal structure of K0.33MoO3 and K0.30MoO3.

Localisation of 4d1 Electrons near Protons in MoO3, Single Crystals (ESR Measurements)

AbstractIt is shown by ESR‐measurements on differently treated single crystals of MoO3 that in these crystals the localisation of molybdenum 4d1 electrons is always connected with the presence of protons. We determine the parameters of the transferred hyperfine interaction tensor.

Amélioration de la méthode des flux, synthèse et purification d'un minéral naturel: La forstérite

It is well known that single crystals of iron-free olivine have numerous applications in geological studies as well as in ESR and infra-red spectroscopy. Previously, clear and stoichiometric single crystals of centimeter size have been grown only by Bridgman or flame-fusion technique with all the incoveniences of the methods.We report growth using fluxes such as PbOV2O5, MoO3Li2O, WO3Li2O. The solubility has been increased with fluxes containing MoO3, Li2O5 and larger crystals have grown. Centimeter-size single crystals of forsterite with uniform composition were obtained after slow-cooling. The morphology of these compounds was the same as native olivines.Impurity concentration was measured by microprobe and optical emission spectrometry. Molybdenum was found only in inclusions. Some crystals doped with Gd3+ and Fe3+ were also studied by ESR techniques to locate the doping ions in the lattice.Inclusions were completely eliminated by heating crystals in a hydrogen atmosphere.

Diffusion of Tc-99m in Neutron Irradiated Molybdenum Trioxide and Its Application to Separation

The dry distillation method was studied for rapid separation of 99mTc from neutron irradiated MoO3. Upon heating, 99mTc produced in MoO3 crystal by the 98Mo(n,r)Mo99m β→ 99mTc process was found to be released by diffusion. From observations made of the deposition temperature, it was concluded that 99mTc was present in the form of 99mTc(IV) in the MoO3 crystal lattice and that it was released in the form of 99mTcO2, which, in air, further oxidized to 99mTc2O7. The release of 99mTc from neutron irradiated MoO3 powder was studied in the temperature range of 480°700°C, and its behavior was found to be in good agreement with the bulk diffusion mechanism based on Fick's law. The diffusion coefficient varied with temperature in compliance with Arrhenius' relation, except in the region of temperatures above 700°C. The separation of 99mTc from MoO3 was performed with a yield higher than 80% upon heating for 30 min at 800°C in air. The decontamination factor for 99Mo was consistently found higher than 105.

Reliability growth and its upper limit : E. P. Virene, Proc. 1968 Ann. Symp. Reliab., Boston, U.S.A., January (1968), p. 265

The influence of niobium on the physicochemical properties of the MoVO system and on its catalytic properties in the oxidation of ethane to ethylene and acetic acid is examined. Solids based on MoV0.4Ox and MoV0.4Nb0.12Oy composition and calcined at 350 or 400 °C were studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. Their reactivity during reduction and reoxidation was examined by in situ XRD and by XPS after pre-treatment. Their stability in air was evaluated by means of Raman spectroscopy during laser heating of particles. Niobium is responsible for both stabilization and nanosize of MoO3 and (VNbMo)5O14 crystals. The high global selectivity to ethylene and acetic acid (90–96 mol%) is related to the presence of both phases while higher activity is owed to nanoparticles. The model already proposed by Merzouki et al. (Stud. Surf. Sci. Catal., 72 (1992) 81) suggesting that MoVNbO catalysts could be made up from (VNbMo)5O14-type microdomains in MoO3 matrix seems still topical.