Secondary phases in Nb-doped BaTiO3 ceramics

In this work, the effect of Nb2O5 addition on the microstructure of BaTiO3 was studied. From XRD diagrams, a diminution in tetragonality parameters with an increase in dopant concentration was observed. In order to determine morphology and composition of secondary phases in niobium-doped barium titanate, EDAX and SEM analyses were carried out. It was found that a concentration of dopant higher than 0.15 mol% leads to fine-grained BaTiO3 without abnormal grain growth. Otherwise, compositions of secondary phases correspond to the titanium-rich region in the BaO-TiO2 phase diagram. Besides, the titanium content in the precipitate increases with the Nb2O5 addition. (C) 2002 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

TiO2-Cu photocatalysts: A study on the long- and short-range chemical environment of the dopant

In this study, the short- and long-range chemical environments of Cu dopant in TiO2 photocatalyst have been investigated. The Cu-doped and undoped TiO2 specimens were prepared by the sol-gel approach employing CuSO4·5H2O and Ti(O-iPr)4 precursors and subjecting the dried gels to thermal treatment at 400 and 500 C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a significantly higher efficiency of Cu-doped samples than that of pure TiO2. The X-ray diffraction results showed the presence of anatase phase for samples prepared at 400 and 500 C. No crystalline CuSO4 phase was detected below 500 C. It was also found that doping decreases the crystallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environment of sulfate changes as a function of thermal treatment, and UV-vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 C sample. X-ray absorption fine structure measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu2+ local order is similar to that of CuSO4, containing, however, oxygen vacancies. X-ray photoelectron spectroscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO4, the presence of Cu1+ and CuO phases, indicating the active role of Cu in the TiO2 lattice. © 2013 Springer Science+Business Media New York.

Luminescence quantum efficiency at 1.5 μm of Er3+-doped tellurite glass determined by thermal lens spectroscopy

Erbium doped tellurite glasses (TeO2 + Li2O + TiO2) were prepared by conventional melt-quenching method to study the influence of the Er3+ concentration on the luminescence quantum efficiency (η) at 1.5 μm. Absorption and luminescence data were used to characterize the samples, and the η parameter was measured using the well-known thermal lens spectroscopy. For low Er3+ concentration, the measured values are around 76%, and the concentration behavior of η shows Er-Er and Er-OH- interactions, which agreed with the measured lifetime values. © 2013 Elsevier B.V. All rights reserved.

Soft-chemical synthesis, characterization and humidity sensing behavior of WO3/TiO2 nanopowders

Tungsten oxide/titania (WO3/TiO2) nanopowders were synthesized by the polymeric precursor method which varied the WO3 content between 0 and 10 mol%. The powders were thermally treated in a conventional furnace and their structural, microstructural and electric properties were evaluated by X-ray diffraction (XRD), Raman spectrometry, N 2 physisorption, NH3 chemisorption, temperature-programmed reduction (TPR), X-ray absorption near-edge spectroscopy (XANES) in situ XANES and extended X-ray absorption fine structure spectroscopy (EXAFS) and transmission electron microscopy (TEM). XRD and Raman spectrometry confirmed the homogeneous distribution of an amorphous WO3 phase in the TiO 2 matrix which stabilized the anatase phase through the generation of [TiO5·V0] or [TiO5·V 0] complex sites. Conventional TPR-H2 (temperature programmed reduction) along with XANES TPR-H2 and XANES TPR-EtOH showed that WO3/TiO2 sample reduction occurs through the formation of these complex clusters. Moreover, the addition of WO3 promoted an increase in the surface acidity of doped samples as revealed by NH3 chemisorption. The WO3/TiO2 bulk-ceramic samples were further used to estimate their potential application in a humidity sensor in the range of 15-85% relative humidity. Probable reasons that lead to the different humidity sensor responses of samples were given based on the structural and surface characterizations. Correlation between the sensing performance of the sensor and its structural features are also discussed. Although all samples responded as a humidity sensor, the W2T sample (2 mol% added WO3) excelled for sensitivity due to the increase in acid sites, optimum mean pore size and pore size distribution. © 2013 Elsevier B.V.

Propriedades elétricas e modelagem da barreira de potencial do sistema varistor à base de SnO2-TiO2

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Analysis of electronic structure of boron nitride nanotubes with different positions of intrinsic impurities

The pristine boron nitride nanotubes have a large direct band gap around 5 eV. This band gap can be engineered by doping. We investigate electronic structure of the doped hexagonal boron nitride (5,5) nanotubes using the linearized augmented cylindrical wave method. In particular, this work focuses on systematical study of the band gap and the density of states around the Fermi-level when the nanotubes are doped by intrinsic impurities of two substitutional boron atoms in a super cell and a comparative analysis of the relative stability of three structures studied here. This corresponds to 3.3% of impurity concentration. We calculate 29 configurations of the nanotubes with different positions of the intrinsic impurities in the nanotube. The band gap and density of states around the Fermi level show strong dependence on the relative positions of the impurity atoms. The two defect sub bands called D^∏(B) appear in the band gap of the pristine nanotube. The doped nanotubes possess p-type semiconductor properties with the band gap of 1.3-1.9 eV.

Estrutura eletrônica e propriedades elétricas fotoinduzidas em filmes finos de SnO2 com dopagem de Sb, e formação de heteroestruturas com TiO2

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Otimização do processo de deposição de filmes TiO2:Mn usando RF magnetron sputtering

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Evidence of magnetoelectric coupling on calcium doped bismuth ferrite thin films grown by chemical solution deposition

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structure and photocatalytic properties of Nb-doped Bi12TiO20 prepared by the oxidant peroxide method (OPM)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Obtenção e caracterização de nanoestruturas puras e dopadas a base de 'TI''O'IND.2' para a aplicação em fotocatálise

Pós-graduação em Química - IQ

Adsorção-fotodegradação do herbicida paraquate em água pela argila Na-Bentonita e por novos materiais TiO2-Bentonita, TiO2/ZnOBentonita, Al/Fe-Bentonita e Al/Fe.Cu-Bentonita

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Wettability behavior of nanotubular TiO2 intended for biomedical applications

Nanotubes have been subject of studies with regard to their ability to promote differentiation of several cells lines. Nanotubes have been used to increase the roughness of the implant surfaces and to improve bone tissue integration on dental implant. In this study TiO2 nanotube layer prepared by anodic oxidation was evaluated. Nanotube formation was carried out using Glycerol-H2O DI(50-50 v/v)+NH4F(0,5 a 1,5% and 10-30V) for 1-3 hours at 37ºC. After nanostructure formation the topography of surface was observed using field-emission-scanning-microscope (FE-SEM). Contact angle was evaluated on the anodized and non-anodized surfaces using a water contact angle goniometer in sessile drop mode with 5 μL drops. In the case of nanotube formation and no treatment surface were presented 39,1° and 75,9°, respectively. The contact angle describing the wettability of the surface is enhanced, more hydrophilic, on the nanotube surfaces, which can be advantageous for enhancing protein adsorption and cell adhesion.

Modificação de eletrodos de carbono vítreo e nanotubos de Ti/TiO2 com aspirinato de cobre (II) para detecção eletroquímica e redução fotoeletrocatalítica de íons nitrito

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)