The effect of cooling rate during hydrothermal synthesis of ZnO nanorods

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The modification of structural and optical properties of nano- and submicron ZnO powders by variation of solvothermal syntheses conditions

Nano- (30-60 nm) and submicron (100-350 nm) ZnO particles were synthesized using solvothermal method at 200 degrees C from an ethanolic solution of zinc acetate dihydrate, applying different reaction conditions, i.e., pH value of precursor and time of the reaction. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance (DR), Raman spectroscopy, and photoluminescence (PL) spectroscopy have been employed for characterization of synthesized ZnO powders. It was shown that the structural, morphological, and optical properties are largely determined by reaction conditions during solvothermal synthesis. The particle crystallinity improves with the decrease of pH value and/or the increase of time of the reaction. The Raman and PL spectra analyses indicate that the oxygen interstitials are dominant intrinsic defects in solvothermally synthesized ZnO powders. It was observed that concentration of defects in wurtzite ZnO crystal lattices slightly changes with the variation of pH value of the precursor and time of the solvothermal reaction. The correlation between structural ordering and defect structure of particles and corresponding growth processes was discussed.

Rietveld refinements of SnO(2) ceramic powders doped with ZnO, WO(3), CoO, Nb(2)O(5) and MoO(3)

Polycrystalline materials of SnO(2) doped with ZnO, WO(3), CoO, Nb(2)O(5), and MoO(3). were synthesized by solid state reaction. X-ray powder diffraction data were collected with Cu K(alpha) radiation from a Rigaku-Rint 2000 rotating anode source. The structural and profile parameters were refined by the Rietveld method using GSAS [2]. The obtained residual parameters are R(wp) = 11,93% and R(Bragg) = 4,19%. The refined profile parameters indicate no anisotropic crystallite microstrain. The refinement results and Fourier differences calculations indicate that the dopants do not occupy interstitial sites in the crystal structure of SnO(2).

The effects of ZnGa2O4 formation on structural and optical properties of ZnO : Ga powders

Gallium-doped zinc oxide (ZnO:Ga 1, 2 3, 4 and 5 at%) samples were prepared in powder form by modifying the Pechini method. The formation of zinc gallate (ZnGa2O4) With the spinel crystal structure was observed even in ZnO:Ga 1 at% by X-ray diffraction. The presence of ZnGa2O4 in ZnO:Ga samples was also evidenced by luminescence spectroscopy through its blue emission at 430 nm, assigned to charge transfer between Ga3+ at regular octahedral symmetry and its surrounding O2- ions. The amount of ZnGa2O4 increases as the dopant concentration increases, as observed by the quantitative phase analysis by the Rietveld method. (C) 2006 Elsevier B.V. All rights reserved.

Microwave Hydrothermal Synthesis and Photocatalytic Performance of ZnO and M:ZnO Nanostructures (M = V, Fe, Co)

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