1,721,031 research outputs found
Surface and Structure Characterization of Some Perovskite-type Powders To Be Used As Combustion Catalysts
No full textSome perovskite-type transition-metal mixed oxide powders active in the combustion catalysis, with formulas LaMO(3) (M = Fe, Cr, Co, and Mn), have been prepared by different methods. Similarly, potential supports for combustion catalysts nearly isostructural with the above ones have been prepared, with compositions SrZrO3 and LaAlO3. Mixed phases with formulas Sr1-xLaxZr1-xMnxO3 have also been investigated. The bulk properties have been studied by XRD, far-IR spectroscopy, and DTA-TG analyses. Morphological properties have been determined by XRD, SEM, and surface area measurements. These phases crystallize after heating at 970 K (except LaFeO3, which is already crystalline after calcination at 770 K) with surface area ranging 10-20 m(2)/g. The solubility of LaMnO3 into SrZrO3 is limited to near 10%. Their surface properties have been investigated by IR spectroscopy that showed a predominantly basic surface character of all these solids
Skeletal Vibrations of Cuprate Superconductor-like Phases - A Comparison of the Ft-fir Spectra of La2-xSrxCuO4, Nd2-xCexCuO4 and RBa(2)Cu(3)O(7-x) (r=ln Or Y) Powders
No full textThe FT-IR/FT-FIR spectra of powders of Nd2-xCexCuO4 and La2-xSrxCuO4 solid solutions and of RBa(2)Cu(3)O(7-x) with R = Y, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb, have been recorded at room temperature. A comparison with the published single-crystal IR data is done. An empirical assignment of the observed bands is proposed on the basis of the factor group analysis and of a discussion of the internal vibrational structure of the CuOx sheets and chains
Thermal stability and structural aspects of Y1-xPrxBa2Cu3On-y solid solution
No full textThe complete Y1-xPrxBa2Cu3O7-y solid solution has been studied from the point of view of thermodynamic and structural propel ties. DTA measurements allowed us to deter mine the trend of the peritectic decomposition temperature and the eutectic one vs. the increasing of Pr content. These data can give some information about the primary crystallisation field of these phases. FT-IR/FT-FIR skeletal characterisation of the solid solution presents the vibrational modes of both YBCO and PrBCO phases; the increasing of one component percentage inside the solution gives rise to a progressive shift of the peaks towards the corresponding frequencies of the end compounds. One of the vibrational modes, assigned to the asymmetric strain of the O-Cu-O units in the O-deficient compounds, seems to be very sensitive to the oxygen content in the samples
Structural, electro-magnetic and catalytic characterisation of the LaMn1-xCuxO3-delta system
No full textThe LaMn1-xCuxO3-delta system has been investigated for the first time from the point of view of the structure in relation to different preparation procedures. Skeletal FTIR spectroscopy has been used in support to XRD characterisation. Oxygen content, magnetic behaviour and resistivity have also been measured. Two compositions have been tested in the catalytic combustion of methane
Vibrational spectra study of Mo(V) phosphates as examples of different geometries of dimolybdenyl species
No full textThree different phosphate structures, alpha -K(2)Mo(2)P(2)O(11), beta -K(2)Mo(2)P(2)O(11) and CdMoPO(6), in which molybdenum(V) octahedra are assembled in different ways, have been studied by vibrational spectroscopy techniques. A correlation is given between crystal structure and infrared and Raman band behaviour which allows identification of vibrational modes sensitive to a particular configuration of molybdenum species. This represents a powerful tool for structure characterisation when amorphous or single layer supported phases are under study
Preparation, characterization and surface structure of coprecipitated high-area SrxTiO2+x(0<=x<=1) powders
No full textPowders with composition SrxTiO2+x (x = 0, 0.02, 0.11, 0.42 and 1) have been prepared by coprecipitation from strontium hydroxide and titanium isopropoxide and have been characterized after drying at 393 K, and after calcination at 773 and 973 K, using XRD, TG-DTA, BET surface area and porosity measurements, FTIR-FTFIR and FT-Raman skeletal vibrational characterization, diffuse reflectance UV-VIS spectroscopy and FTIR spectra of the hydroxy groups and of adsorbed pyridine and CO2. Strontium was found to inhibit anatase crystallization, sintering and transformation to rutile. Strontium tended to be deposited at the surface of anatase and gave rise to a decrease of the surface acidity and an increase of surface basicity. Moreover, it shifted the absorption edge of anatase to higher energies. For x = 1, the truly cubic SrTiO3 perovskite phase was produced at room temperature with high surface area. The surface of SrTiO, was definitely basic, with only strontium and oxygen ions exposed at the surface, and hydrogen impurities in the bulk
Enthalpy measurements on Nd2-xCexCuO4: under oxygen pressure and thermodynamic potentials calculation
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