Structural and morphological characterization of Pb1-xBaxTiO3 thin films prepared by chemical route: An investigation of phase transition

Detailed room temperature micro-Raman scattering, X-ray diffraction, atomic force microscopy and specular reflectance infrared Fourier transform spectroscopy studies were carried out on soft chemical by processed Pb1-xBaxTiO3 thin films. The micro-Raman spectra pointed the existence of a stable tetragonal ferroelectric phase in the entire composition range (0 < x <= 1). The infrared reflectance spectra showed that the frequency of several peaks decreases as the Ba2+ concentration increases. These features are correlated to a decrease in the tetragonal distortion of the TiO6 octahedra as the Ba2+ concentration increases. Furthermore, as x increases from 0.70 to 1.0, the Raman spectrum shows an evolution towards the well-known Raman spectrum of the tetragonal BaTiO3. Therefore, we demonstrated that the combination of solid solution PbTiO3-BaTiO3 with a grain size in the order of 30-40 nm supports the tetragonal ferroelectric phase at room temperature. (C) 2007 Elsevier B.V. All rights reserved.

Solid-state reactions of mercury with pure noble metals - Part 2. Mercury-iridium system

Thermogravimetry, cyclic voltammetry and other analytical techniques were used to study the reactions of mercury with pure iridium. The results allowed to suggest when subjected to heat or anodic stripping voltammetry an electrodeposited mercury film reacts with Ir substrate and at least three mass loss steps and three peaks appear in the mercury desorption process. The first two were attributed to Hg(0) species removal like a mercury bulk and a mercury monolayer. The last can be ascribed to the mercury removal from a solid solution with iridium.

Influence of Ca concentration on the electric, morphological, and structural properties of (Pb,Ca)TiO3 thin films

Pb1-xCaxTiO3 (0.10less than or equal toxless than or equal to0.40) thin films on Pt/Ti/SiO2/Si(100) substrates were prepared by the soft solution process and their characteristics were investigated as a function of the calcium content (x). The structural modifications in the films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate a decrease in lattice tetragonality with the increasing content of calcium in these films. Raman spectra exhibited characteristic features of pure PbTiO3 thin films. Variations in the phonon mode wave numbers, especially those of lower wave numbers, of Pb1-xCaxTiO3 thin films as a function of the composition corroborate the decrease in tetragonality caused by the calcium doping. As the Ca content (x) increases from 0.10 to 0.40, the dielectric constant at room temperature abnormally increased at 1 kHz from 148 to 430. Also calcium substitution decreased the remanent polarization and coercive field from 28.0 to 5.3 muC/cm(2) and 124 to 58 kV/cm, respectively. These properties can be explained in terms of variations of phase transition (ferroelectric-paraelectric), resulting from the substitution the lead site of PbTiO(3)for the nonvolatile calcium. (C) 2002 American Institute of Physics.

Hierarchical Assembly of CaMoO4 Nano-Octahedrons and Their Photoluminescence Properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural refinement and photoluminescence properties of irregular cube-like (Ca-1_Cu-x(x))TiO3 microcrystals synthesized by the microwave-hydrothermal method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Completeness of beta-phase decomposition reaction in Cu-Al-Ag alloys

The completeness of beta-phase decomposition reaction in the Cu-11wt%Al-xwt%Ag alloys (x = 0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that beta-phase transformations are highly dependent on cooling rate and on the presence of Ag. on slow cooling, the silver presence prevents the beta- and beta(1)-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures.

Crystallization study of SrSnO3:Fe

Alkaline earth stannates have recently become important materials in ceramic technology due to its application as humidity sensor. In this work, alkaline earth stannates doped with Fe3+ were synthesized by the polymeric precursor method, with calcination at 300 A degrees C/7 h and between 400 and 1100 A degrees C/4 h. The powder precursors were characterized by TG/DTA after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, infrared spectroscopy, and UV-vis spectroscopy. Results confirmed the formation of the SrSnO3:Fe with orthorhombic perovskite structure, besides SrCO3 as secondary phase. Crystallization occurred at 600 A degrees C, being much lower than the crystallization temperature of perovskites synthesized by solid state reaction. The analysis of TG curves indicated that the phase crystallization was preceded by two thermal decomposition steps. Carbonate elimination occurred at two different temperatures, around 800 A degrees C and above 1000 A degrees C.

SrSnO3:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO3 by the polymeric precursor method, with calcination between 250 and 700 A degrees C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 A degrees C for SrSnO3 and SrSn0.99Nd0.01O3. For Sr0.99Nd0.01SnO3, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 A degrees C, while a XRD patterns showed a crystalline material after calcination at 250 A degrees C.

Spherical particles of phenolic resin treated with iron oxide

This paper describes the preparation and characterization of phenolic resins' thermospheres covered by a magnetic phase of iron oxide. The thermospheres were prepared by allowing phenol and formaldehyde to react under dispersion polymerization conditions and the iron oxide phase was incorporated in situ onto the phenolic resin particles by adding concentrated NH3 to FeCl2 in DMSO. This reaction was conducted at 70 degrees C under nitrogen atmosphere in a controlled temperature vessel, and the modified resin was isolated and dried in vacuo. Both pure and modified resins were characterized by DRX, TG- DTA, and MEV/ EDX. The modified particles were attracted by a magnetic field, indicating the fixation of magnetic iron oxide. No diffraction peaks were observed in DRX analysis; thermal analysis ( DTA) of both pure and modified resins presented exothermic events between 300 and 680 degrees C, and 300 and 570 degrees C, respectively, indicating the microstructure of the resin was modified after the treatment. Thermogravimetric analysis ( TGA) of the pure resin registered a 2.0% residue, compared to 8.0% for the modified resin. These residues correspond to about 7.0% of fixed iron oxide. MEV/ EDX analyses confirm the modification of the resins by the process of fixing iron oxide.

Thermoanalytical study of some anti-inflammatory analgesic agents

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

Ceramic raw materials from the State of Maranhao, Brazil. Part 1: chemical and mineralogical characterization and technological properties of clays from Sao Luis, Rosario, Pinheiro and Mirinzal

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)