Ferroelectric switching and dielectric response of P(VDF-TrFE)/PMMA blends

The ferroelectric and the dielectric behaviors of binary blends formed by an equi-molar Poly(vinylidene fluoride trifluoroethylene) copolymer [P(VDF-TrFE)] and Poly(methyl methacrylate) [PMMA] were investigated, for several PMMA compositions. For 40 wt.% or more PMMA contents, the blends are completely amorphous. Below this value, they crystallize in the usual Cm2m polar structure of P(VDF-TrFE). The ferroelectric switching characteristics and the dielectric response of the blends demonstrate the formation of dynamically stable ferroelectric domains. Moreover, the blended films are highly transparent in the optical region. Therefore, thin films of these binary blends are good candidates as host materials for nonlinear optical applications.

Morphological modifications and surface amorphization in ZnO sonochemically treated nanoparticles

Application of nanoscale materials in photovoltaic and photocatalysis devices and photosensors are dramatically affected by surface morphology of nanoparticles, which plays a fundamental role in the understanding of the physical and chemical properties of nanoscale materials. Zinc oxide nanoparticles with an average size of 20 nm were obtained by the use of a sonochemical technique. X-ray diffraction (XRD) associated to Rietveld refinements and transmission electron microscopy (TEM) were used to study structural and morphological characteristics of the samples. An amorphous shell approximately 10 nm thick was observed in the ultrasonically treated sample, and a large reduction in particle size and changes in the lattice parameters were also observed. © 2012 Elsevier B.V. All rights reserved.

Syntheses of bismuth titanate templates obtained by the molten salt method

Bismuth titanate templates (Bi4Ti3O12) were synthesized by the molten salt method in Na2SO4 and K2SO4 fluxes, using an amorphous Bi4Ti 3O12 precursor and a mechanically mixed Bi 2O3+TiO2 mixture as the starting materials. The templates were characterized by means of X-Ray Diffraction, FT-IR, FT-Raman, FEG-SEM and TEM. The templates are free of secondary phases and present orthorhombic structure with orientation in the c-plane. FT-IR suggests no traces of sulfate groups revealing that the molten salt synthesis was beneficial for elimination of inorganic species and for the arrangement of individual nanocrystals into ordered lattices. FEG-SEM analyses of BIT templates revealed that most of the grains were homogeneous with a length of 3.1 μm and a width of 0.3 μm and had plate-like morphology. TEM investigations show that the c-axis of the perovskite units is parallel to the thickness direction of the grains and no liquid-phase was formed during BIT phase formation. © 2013 Elsevier Ltd and Techna Group S.r.l.

Estudo da fotossensibilidade de materiais híbridos de sílica dopados com heteropoliânions de tungstênio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Geração de segundo harmônico em vidros teluritos TeO2 – LiNbO3

Pós-graduação em Ciência dos Materiais - FEIS

Physicochemical aspects involved in methotrexate release kinetics from biodegradable spray-dried chitosan microparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.

Biochemical and microbiological characteristics of in situ biofilm formed on materials containing fluoride or amorphous calcium phosphate

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

Structure and Physical Properties of EVA/Starch Precursor Materials for Foaming Applications

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

Evaluation of Bulk and Surfaces Absorption Edge Energy of Sol-Gel-Dip-Coating SnO2 Thin Films

The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition.

Development of amorphous carbon protective coatings on poly(vinyl)chloride

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

Relationship between grain-boundary capacitance and bulk shallow donors in SnO2 polycrystalline semiconductor

The relationship between grain-boundary capacitance and extrinsic shallow donors caused by Nb addition to SnO2 center dot COO binary polycrystalline system has been investigated by means of combined techniques such as I-V characteristic response, complex impedance and capacitance analysis and electrostatic force microscopy. The estimated role of the Nb doping is to increase the concentration of shallow donors that are capable of enhancing the electronic donation to grain-boundary acceptors. This effect leads to the formation of potential barriers at grain boundaries with a simultaneous increase of grain-boundary capacitance and non-Ohmic features of the polycrystalline device doped with Nb atoms.

Coloring ionic trapping states in WO3 and Nb2O5 electrochromic materials

Complex electro-optical analysis is a very useful approach to separate different kinetic processes that occur during ionic insertion reactions in electrochromic oxide materials. In this paper, we use this type of combined technique to investigate ionic and optical changes in different oxide host systems, i.e., in two oxide hosts, specifically WO3 and Nb2O5. A comparison of their electro-optical responses revealed the presence of an ionic trapping contribution to the kinetics of the coloring sites, which was named here as coloring ionic trapping state. As expected, this coloring trapping process is slower in Nb2O5 since the reduction potential of Nb2O5 is more negative (more energy is needed for a higher degree of coloration). A phenomenological solid-state model that encompasses homogeneous charge transfer and valence trapping was proposed to explain the coloring ionic trapping process. Basically the model is able to explain how ionic dynamics at low frequency region, i.e., the slower kinetic step, controls the coloring kinetics, i.e., how it is capable to regulate the coloring rates.Optical transient analyses demonstrated the possibility of the presence of more than one coloring ionic trap, indicating the complexity of the processes involved in coloration phenomenon in metal oxide host systems. (C) 2008 Published by Elsevier Ltd.

SnO2 nanoparticles functionalized in amorphous silica and glass

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nanocomposites materials generated from a spray

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)