Hot-pressed 9.5/65/35 PLZT prepared by the polymeric precursor method

A 9.5/65/35 PLZT ceramic with a Pb-0.905 La-0.095 (Zr-0.65 Ti-0.35)(0.976) O-3 + 35 w% PbO formula was prepared using the Pechini method for powder preparation and two-step sintering in an oxygen atmosphere. Thr first step consisted of sintering at 1200 degrees C for 4 h with slow heating and cooling rates. The second step consisted of hot pressing at 1200 degrees C for 3 h, with slow heating and cooling rates and pressing pressures of 20 MPa (initial pressure) and 40 MPa (at sintering temperature). Investigations were made of the powder phase formation and powder morphology, i.e. The structure of sintered and hot-pressed PLZT ceramics. SEM microstructural analyses were carried out on the sintering and hot-pressing processes. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Synthesis of nanocrystalline tetragonal zirconia by a polymeric organometallic method

A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia-12 mol% ceria ceramic powders, the influence of the main process variables (citric acid-ethylene glycol ratio, citric acid-total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single-phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m(2) g(-1) Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions. Copyright (C) 1999 John Wiley & Sons, Ltd.

Ferroelectric materials with photoluminescent properties

Amorphous LiNbO3 thin films processed by polymeric precursor method exhibited efficient luminescence at room temperature. The films were deposited on silicon substrates and treated at 200degreesC for different times. The photoluminescence emission yield decreases with the increase of the treatment time and disappears for crystalline films. A theoretical-experimental study was performed on amorphous and crystalline materials to understand the influence of the defects on the photoluminescence properties. The theoretical band gap obtained by the difference of energy between the HOMO and LUMO levels is larger for crystalline structure when compared with amorphous material. This result, which is in agreement with experimental band gaps obtained from optical measurements, revealed the emergence of new electronic levels for the amorphous material, which are localized in the wide band gap of the crystalline structure. These new electronic levels may explain the photoluminescence observed at room temperature for LiNbO3 amorphous films.

Characterization of nickel doped Zn7Sb2O12 spinel phase using Rietveld refinement

Zn7Sb2O12 is known to adopt an inverse spinel crystal structure, in which Zn2+ occupies the eight tetrahedral positions and Sb5+ and Zn2+ randomly occupy the 16 octahedral positions. Samples of Zn7-xNixSb2O12 (X = 0, 1, 2, 3, and 4) were synthesized using a modified polymeric precursor method, known as the Pechini method. The crystal structure of the powders was characterized by Rietveld refinement with X-ray diffraction data. The results show that for X = 0, 1, and 2 Ni substitutes for Zn2+ in the octahedral sites, and that for X = 3 and 4 it is assumed that Ni2+ replaces Zn2+ ions in both the octahedral and tetrahedral positions. It is also observed for x = 3 and 4 the formation of two spinel phases. (C) 2003 International Centre for Diffraction Data.

Thermal and structural investigation of SnO2/Sb2O3 obtained by the polymeric precursor method

SnO2-based materials are used as sensors, catalysts and in electro-optical devices. This work aims to synthesize and characterize the SnO2/Sb2O3-based inorganic pigments, obtained by the polymeric precursor method, also known as Pechini method (based on the metallic citrate polymerization by means of ethylene glycol). The precursors were characterized by thermogravimetry (TG) and differential thermal analysis (DTA). After characterization, the precursors were heat-treated at different temperatures and characterized by X-ray diffraction. According to the TG/DTA curves basically two-step mass loss process was observed: the first one is related to the dehydration of the system; and the second one is representative to the combustion of the organic matter. Increase of the heat treatment temperature from 500 to 600 degrees C and 700 degrees C resulted higher crystallinity of the formed product.

Influence of the network former on the properties of magnesium spinels

Undoped and/or doped with 1 mol% of Co2+ Mg2TiO4 and Mg2SnO4 powders were synthesized by the polymeric precursor method. The influence of the network former (Sn4+ or Ti4+) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg2TiO4 crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg2SnO4 has.

High sinterability of Ca-PZT, synthesized by polymeric and partial oxalate process

This study includes Ca-PZT in the morphotropic phase boundary, MPB process combining the Pechini method, (ZT) and the Partial oxalate method (Ca-PZT) by obtaining single phase particles of ZT phase with a high specific surface area (similar to 110 m(2)/g at 550 degrees C) and narrow particle size distribution. Lead and calcium oxalates were precipitated onto the ZT particle surface and reacted to a solid state interface ZT/Ca-PZT/PbO-CaO. A deviation of a coexistence region from F-T- and F-R-phases to F-R-phase (Zr rich region) was observed. Strong surface area reduction occurs by Ca-PZT crystallization at about 700 degreesC, and demonstrated high sinterability (2.40 m(2)/g - 350 nm) with apparent densities near to 99.9%. Different processing methods did not demonstrate superior results. Studies of calcined powder shows a high sinterability of powder calcined 3 h at 700 degrees C and sintered 3 h at 1000 degreesC coming up to 99.8% of relative density. (C) 2001 Kluwer Academic Publishers.

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.

The influence of temperature on the color of TiO2:Cr pigments

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Development of metal oxide nanoparticles by soft chemical method

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

Crystallographic, dielectric and optical properties of SrBi2Ta2O9 thin films prepared by the polymeric precursor method

Strontium bismuth tantalate thin films were prepared on several substrates (platinized silicon (PvTi/SiO2/Si), n-type (100)-oriented and p-type (111)-oriented silicon wafers, and fused silica) by the solution deposition method. The resin was obtained by the polymeric precursor method, based on the Pechini process, using strontium carbonate, bismuth oxide, and tantalum ethoxide as starting reagents. Characterizations by XRD and SEM were performed for structural and microstructural evaluations. The electrical measurements, carried on the MFM configuration, showed P-r values of 6.24 muC/cm(2) and 31.5 kV/cm for the film annealed at 800 degreesC. The film deposited onto fused silica and treated at 700 degreesC presented around 80 % of transmittance.

Crystallographic properties of KSr2Nb5O15

Nanostructured KSr2Nb5O15 oxide was synthesized by the polymeric precursor method, a chemical synthesis route based on the Pechini's method. The X-ray diffraction (XRD) pattern of the calcined powder at 1150 degreesC were performed in the angular range 5 less than or equal to 20 less than or equal to 120degrees with a 0.02degrees step and a fixed counting time of 30 s. The XRD data were analyzed by the Rietveld refinements using the FullProf software. The results C showed a tetragonal system with the tetragonal tungsten bronze structure (TTB) type (a = 12.4585 (2) Angstrom and c = 3.9423 (6) Angstrom, V = 611,90 (2) Angstrom). In this work, the sites occupancy by the K+ and Sr2+ cations on the TTB type structure were determined. The thermal parameters (B) were analyzed. (C) 2004 Elsevier B.V. All rights reserved.

Determination of the local site occupancy of Eu3+ ions in ZnAl2O4 nanocrystalline powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of the modifier on the short and long range disorder of stannate perovskites

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO(3)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)