Search results for "Diffraction"
showing 10 items of 1584 documents
Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies.
2008
The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. A…
New insights in the formation of silanol defects in silicalite-1 by water intrusion under high pressure.
2010
International audience; The "water-silicalite-1" system is known to act as a molecular spring. The successive intrusion-extrusion cycles of liquid water in small crystallites (6 × 3 × 0.5 μm(3)) of hydrophobic silicalite-1 were studied by volumetric and calorimetric techniques. The experiments displayed a decrease of the intrusion pressure between the first intrusion-extrusion cycle and the consecutive ones, whereas the extrusion pressures remained unchanged. However, neither XRD studies nor SEM observations revealed any structural and morphological modifications of silicalite-1 at the long-range order. Such a shift in the value of the intrusion pressure after the first water intrusion-extr…
High-pressure and high-temperature X-ray diffraction studies of scheelite BaWO4
2009
International audience; We carried out high-pressure (HP) and high-temperature (HT) in situ ADXRD synchrotron measurements in barium tungstate (BaWO4 ) up to 7.5 GPa and 800 K. Coexistence of the scheelite and fergusonite structures was found beyond 7 GPa, both at room temperature and HT, suggesting a polymorphism zone in the P –T phase diagram. The experiments are complemented by thermodynamic calculations within the quasi-harmonic approximation. At ambient pressure, a volume thermal expansivity of 9.5 × 10− 6 K−1 was obtained for scheelite BaWO4 . At HP, the thermal expansivity of the fergusonite doubles that of scheelite. Theoretical equation of state curves at HP and HT are also present…
A structural investigation of titanium dioxide photocatalysts
1991
Abstract A study of the structure and the morphology of a titanium dioxide photocatalyst (Degussa P25) reveals multiphasic material consisting of an amorphous state, together with the crystalline phases anatase and rutile in the approximate proportions 80 20 . Transmission electron microscopy provides evidence that some individual particles are a mixture of the amorphous state with either the anatase phase or with the rutile phase, and that some particles, which are mostly anatase, are covered by a thin overlayer of rutile which manifests its presence by the appearance of Moire fringes. The photocatalytic activity of this form of titanium dioxide is reported as being greater than the activi…
Reactive direct current magnetron sputtered TiO2 thin films with amorphous to crystalline structures.
2008
International audience; TiO2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, td, and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO2 was obtained for the shortest deposition time, td=15 min. Increasing td up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO2, as was revealed by complementary XRD patterns and Raman spectra…
Mesocrystalline Cr and Sb-codoped anatase visible-light-driven photocatalyst
2018
Abstract We report on the synthesis, characterization and visible-light-driven photocatalytic activity of mesocrystalline Cr- and Sb-codoped anatase nanoparticles. Discrete and morphologically well-defined assemblies of anatase nanoparticles sized below 100 nm × 50 nm were prepared by hydrothermal aging of aqueous solutions containing titanium alkoxide, chromium acetylacetonate, antimony acetate and triethanolamine (TEOA) as stabilizer. The as-prepared and TEOA-free doped nanoparticles showed similar crystallographic parameters and spectroscopic features. The incorporation of Cr and Sb dopant cations into the anatase nanoparticles was evaluated by Rietveld refinement of X-ray diffraction pa…
Mesocrystalline anatase nanoparticles synthesized using a simple hydrothermal approach with enhanced light harvesting for gas-phase reaction
2018
Mesocrystalline TiO2 nanoparticles were synthesized using a hydrothermal approach. A simple two-step procedure at low temperature (<140 °C) allowed the nucleation of primary particles sized 2–4 nm and their subsequent assembly as almost spherical aggregates sized ≈20 nm. X-ray powder diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) studies, and HRTEM studies confirmed anatase as the unique TiO2 crystalline phase. The mesocrystalline structure of the anatase aggregates was clearly evidenced by HRTEM and SAED results. The mesocrystalline nanopowders exhibit a mesoporous structure with a surface area and pore volume of 63.5 m2 g−1 and 0.22 cm3 g−1, respectively. Ultraviolet …
Hydrothermal-mediated synthesis of orange Cr, Sb-containing TiO 2 nano-pigments with improved microstructure
2017
Abstract A hydrothermal-mediated via was developed to prepare discrete, non-aggregated Cr,Sb-doped rutile nano-pigments. After annealing the Cr- and Sb-containing TiO2 anatase nanocrystals obtained by hydrothermal aging the nano-pigments Cr,Sb-TiO2 were characterized with the aid of X-ray diffraction (XRD) including lattice parameter and crystallite size determination, Raman spectroscopy, field emission scanning and transmission electron microscopies (FESEM and TEM, respectively) including energy-dispersive X-ray (FESEM/EDX) spectroscopy, high resolution transmission electron microscopy (HRTEM) including selected area electron diffraction (SAED), ultraviolet–visible diffuse reflectance (UV–…
Phase formation in mixed TiO2-ZrO2 oxides prepared by sol-gel method
2011
Pure titania, zirconia, and mixed oxides (3—37 mol.% of ZrO2) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the presence of 3—13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature increase above 700 C. The mixed oxide with 37 mol.% of ZrO2 treated at 550 C shows a new single amorphous phase with a surface area of the…
"Identification of mixed bromidochloridotellurate anions in disordered crystal structures of (bdmim)2[TeX2Y4] (X, Y = Br, Cl; bdmim = 1-butyl-2,3-dim…
2013
Abstract The discrete mixed [TeBrxCl6−x]2− anions in their disordered crystal structures have been identified by using the phases prepared by the reaction of 1-butyl-2,3-dimethylimidazolium halogenides (bdmim)X with tellurium tetrahalogenides TeX4 (X = Cl, Br) as examples. Homoleptic (bdmim)2[TeX6] [X = Cl (1), Br (2)] and mixed (bdmim)2[TeBr2Cl4] (3), and (bdmim)2[TeBr4Cl2] (4) are formed depending on the choice of the reagents, and their crystal structures have been determined by single-crystal X-ray diffraction. The coordination environments of tellurium in all hexahalogenidotellurates are almost octahedral. Because of the crystallographic disorder, the mixed [TeBr2Cl4]2− and [TeBr4Cl2]2…