Search results for " magnetic materials"
showing 10 items of 4666 documents
Influence of Amorphous TiO2-x on Titania Nanoparticle Growth and Anatase-to-Rutile Transformation
2012
Amorphous TiO2-x formed together with precursors and anatase nuclei, during TiCl4 hydrolysis at soft conditions, influences both crystal growth and phase stability. The highly defective nanoparticles of anatase grow by reaction of their basic hydroxyls with acidic ones of TiO2 precursor species. The growth of anatase crystals, however, is affected by their interactions with simultaneously formed amorphous TiO2-x which increasingly covers the particles hindering the anatase-precursor contact. The interactions among anatase and amorphous and precursor components have been studied by H-1-MAS (magic angle spinning) NMR spectroscopy. The interaction between acid and basic hydroxyls favors the fo…
Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films
2006
Photoactive films consisting of pure anatase, brookite or rutile TiO2 were prepared by dip coating from water dispersions obtained by using TiCl4 as the precursor under similar mild experimental conditions
Investigation on sol–gel synthesized Ag-doped TiO2 cermet thin films
2005
Abstract Undoped TiO 2 and Ag–TiO 2 (up to 23 at.% Ag) cermet thin films and polycrystalline powders have been prepared by sol–gel process. Their structure, composition, surface morphology and optical properties have been investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and ultraviolet–visible spectroscopy (UV–VIS spectroscopy). It has been observed that while Ag does not form a solid solution with TiO 2 , it promotes the anatase to rutile phase transformation. The transformation temperature decreases from 827 °C for undoped TiO 2 to about 650 °C fo…
Removal of Surface Oxygen Vacancies Increases Conductance Through TiO(2) Thin Films for Perovskite Solar Cells
2019
[Image: see text] We report that UV–ozone treatment of TiO(2) anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV–ozone-treated TiO(2) anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO(2) anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV–ozone treatment results in a reduced number of oxygen…
TiO2 nanostructures prepared by ferrocene/cobalt catalyst agents
2008
We present the growth and characterization of TiO2 nanocrystals. Nanostructured growth is obtained in a low-pressure CVD system by using an organometallic precursor Ti(OC3H7)4 as both the Ti and O source catalyzed by both ferrocene (an organometallic precursor) and cobalt metallic clusters prepared by the microwave-assisted polyol method. Two kinds of TiO2 structures were obtained in the cobalt clusters: a) pine-tree like (with short-leaf structure) and b) long-leaf structures as large as a few micrometers in size and both under 10 nm in thickness. Long-leaf TiO2 structures were grown at cobalt grain boundaries. For the growth conditions utilized, the TiO2 structures are composed of both an…
Tailoring the Structural, Optical, and Photoluminescence Properties of Porous Silicon/TiO2 Nanostructures
2015
The structural, optical, and photoluminescence properties of porous silicon (PSi)/titanium dioxide (TiO2) nanostructures were investigated. PSi structures consisting of macro- and mesoporous layers were fabricated by metal-assisted chemical etching, and then TiO2 was introduced inside the PSi matrix using the atomic layer deposition technique. We performed scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy, ellipsometry, and photoluminescence (PL) spectroscopy to characterize the prepared and annealed PSi/TiO2 nanostructures. TEM and Raman analyses revealed that TiO2 had a crystalline anatase stru…
Photocatalytic thin films of TiO2 formed by a sol-gel process using titanium tetraisopropoxide as the precursor
2008
Abstract Thin TiO 2 films were prepared with the dip-coating technique by using sols deriving from titanium tetraisopropoxide. TiO 2 films were formed on glass substrates previously covered by a SiO 2 layer obtained from a tetraethylortosilicate sol. The films, after a thermal treatment at 673 K, mainly consisted of TiO 2 anatase. The samples were characterised by X-ray diffraction, UV–Vis spectroscopy, scanning electron microscopy and atomic force microscopy. The photoactivity of the various films was tested by using as probe reaction the photo-oxidation of 2-propanol in gas-solid regime. The photoreactivity results indicated that the TiO 2 films were efficient for degrading 2-propanol und…
Photocatalytic activity of anatase-nickel ferrite heterostructures
2015
The simple co-precipitation route was used to couple commercial TiO2 anatase nanopowder with nickel ferrite (NiFe2O4). The morphology and the crystalline structure of composite nanoparticles were characterised by TEM, N2 adsorption-desorption, XRD and Rietveld refinement, XPS and XAS. The optical and magnetic properties were investigated. After co-precipitation NiFe2O4 nanoparticles, composed of spinel ferrite crystal phase, were formed on the surface of TiO2 anatase nanopowder. The TiO2/NiFe2O4 composite oxide demonstrated large specific surface area, high visible light absorption efficiency and efficient charge carrier separation, compared to pristine anatase TiO2 or pristine NiFe2O4, rep…
The Electronic Structure of Hexagonal BaCoO3
1999
Abstract TB–LMTO–ASA band structure calculations within the local spin density approximation have been performed to explain the magnetic and transport properties of BaCoO3. The calculations predict a magnetic and metallic ground state as energetically favored. BaCoO3 shows no long-range magnetic ordering, however, and only poor conductivity. The magnetic energy is low and the compound shows glassy susceptibility behavior at low temperatures. From the band structure we find Mott–Hubbard localization to be unlikely, and instead propose Anderson localization as a possible origin of the observed behavior. Calculations on slightly distorted structures exclude the possibility of a Peierls distort…
Polar bosons in one-dimensional disordered optical lattices
2013
We analyze the effects of disorder and quasi-disorder on the ground-state properties of ultra-cold polar bosons in optical lattices. We show that the interplay between disorder and inter-site interactions leads to rich phase diagrams. A uniform disorder leads to a Haldane-insulator phase with finite parity order, whereas the density-wave phase becomes a Bose-glass at very weak disorder. For quasi-disorder, the Haldane insulator connects with a gapped generalized incommesurate density wave without an intermediate critical region.