Corrente, Brazil
Corrente, Brazil

Time filter

Source Type

Parija B.,National Institute of Technology Rourkela | Rout S.K.,BIT | Cavalcante L.S.,São Paulo State University | Panigrahi S.,National Institute of Technology Rourkela | And 3 more authors.
Ceramics International | Year: 2013

Lead-free solid solutions (1-x)Bi0.5Na0.5TiO 3 (BNT)-xBaZr0.25Ti0.75O3 (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1-x(BNT)-x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO3) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05. © 2012 Elsevier Ltd and Techna Group S.r.l.

Goncalves R.F.,Federal University of São Paulo | Cavalcante L.S.,UESPI | Nogueira I.C.,Federal University of Maranhão | Longo E.,São Paulo State University | And 7 more authors.
CrystEngComm | Year: 2015

CaWO4:Eu3+ microcrystals (with 0, 1, 2 and 4 mol% Eu3+) were synthesized by a co-precipitation (CP) method and grown in a microwave-assisted hydrothermal (MAH) system at 130 °C for 30 min. X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near edge spectroscopy (XANES), Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopy indicated that all of the microcrystals have a scheelite-type tetragonal structure without deleterious phases. Structural refinement data were employed to model the [CaO8], [EuO8] and [WO4] clusters. XANES spectra confirmed that the presence of deltahedral [EuO8] clusters promotes small distortions of neighbouring tetrahedral [WO4] clusters in a global tetragonal lattice. Field emission scanning electron microcopy (FE-SEM) images revealed that the replacement of Ca2+ by Eu3+ ions changed the particles' shapes, resulting in the different morphologies of the microcrystals. UV-vis diffuse reflectance spectra indicated a reduction in the optical band gap with the replacement of Ca2+ by Eu3+ ions. The photoluminescence (PL) properties of the Eu3+ ions in CaWO4 were studied as well as the chromaticity coordinates and lifetimes of these compounds. This journal is © The Royal Society of Chemistry 2015.

Cavalcante L.S.,São Paulo State University | Batista F.M.C.,Federal University of Piauí | Almeida M.A.P.,Federal University of São Carlos | Rabelo A.C.,Federal University of São Carlos | And 7 more authors.
RSC Advances | Year: 2012

Barium praseodymium tungstate (Ba 1-xPr 2x/3)WO 4 crystals with (x = 0, 0.01, and 0.02) were prepared by the coprecipitation method. These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements, Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopies. The shape and size of these crystals were observed by field emission scanning electron microcopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. Moreover, we have studied the photocatalytic (PC) activity of crystals for degradation of rhodamine B (RhB) dye. XRD patterns, Rietveld refinements data, FT-Raman and FT-IR spectroscopies indicate that all crystals exhibit a tetragonal structure without deleterious phases. FT-Raman spectra exhibited 13 Raman-active modes in a range from 50 to 1000 cm -1, while FT-IR spectra have 8 infrared active modes in a range from 200 to 1050 cm -1. FE-SEM images showed different shapes (bonbon-, spindle-, rice- and flake-like) as well as a reduction in the crystal size with an increase in Pr 3+ ions. A possible growth process was proposed for these crystals. UV-vis absorption measurements revealed a decrease in optical band gap values with an increase of Pr 3+ into the matrix. An intense green PL emission was noted for (Ba 1-xPr 2x/3)WO 4 crystals (x = 0), while crystals with (x = 0.01 and 0.02) produced a reduction in the wide band PL emission and the narrow band PL emission which is related to f-f transitions from Pr 3+ ions. High photocatalytic efficiency was verified for the bonbon-like BaWO 4 crystals as a catalyst in the degradation of the RhB dye after 25 min under UV-light. Finally, we discuss possible mechanisms for PL and PC properties of these crystals. This journal is © 2012 The Royal Society of Chemistry.

Gouveia A.F.,Federal University of São Carlos | Sczancoski J.C.,São Paulo State University | Ferrer M.M.,Federal University of São Carlos | Lima A.S.,São Paulo State University | And 5 more authors.
Inorganic Chemistry | Year: 2014

In this paper, we investigate a correlation between theoretical calculations and experimental data to explain the electronic structure and optical properties of silver molybdate (β-Ag2MoO4) microcrystals synthesized by the microwave-assisted hydrothermal method. X-ray diffraction, Rietveld refinement, and micro-Raman spectroscopy confirmed that these microcrystals crystallize in a spinel-type cubic structure. Field-emission scanning electron microscopy images revealed that the processing temperatures influence in the final shape of microcrystals. Optical properties were analyzed by ultraviolet-visible diffuse reflectance spectroscopy; the increase in the optical band gap energy (Egap) (from 3.24 to 3.31 eV) with processing temperature is associated with the reduction of intermediary energy levels. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level were conducted. The calculated band structure revealed an indirect Egap of approximately 4.00 and 3.34 eV for the β-Ag2MoO4 without and with the formation of defects, respectively. Theoretical calculations based on density of states and electron density maps were employed to understand the polarization phenomenon induced by structural defects in the β-Ag2MoO4 crystals. Finally, photoluminescence properties at room temperature of β-Ag 2MoO4 microcrystals were explained by the charge-transfer mechanism involving tetrahedral [MoO4] clusters. © 2014 American Chemical Society.

Badapanda T.,Orissa Engineering College, Bhubaneswar | Senthil V.,Orissa Engineering College, Bhubaneswar | Anwar S.,CSIR - Institute of Minerals And Materials Technology | Cavalcante L.S.,UESPI | And 2 more authors.
Current Applied Physics | Year: 2013

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr 0.1Ti0.9]O3 (BZT) polymer-ceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement, cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymer-ceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (εr) and the dielectric loss (tan δ) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymer-ceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors. © 2013 Elsevier B.V. All rights reserved.

Sediyama M.A.N.,EPAMIG | dos Santos M.R.,UESPI | Vidigal S.M.,EPAMIG | Pinto C.L.O.,EPAMIG | Jacob L.L.,EPAMIG
Revista Brasileira de Engenharia Agricola e Ambiental | Year: 2014

Swine bio-fertilizer can be used as organic fertilizer, based on the criteria of quality and quantity necessary for the soil and plant. The objective of this study was to evaluate nutrition and yield of two colored pepper cultivars, fertilized with swine bio-fertilizer, using organic cultivation techniques. Two hybrid cultivars were evaluated: Amanda (yellow fruit) and Rubia (red fruit) and four bio-fertilizer doses (0, 30, 60 and 120 m3 ha-1) applied in the soil before planting and under cover after seedling transplant. There was response for bio-fertilizer doses with positive effects on the nutrition of pepper plant and fruit yield. Cultivar Rubia presented a higher SPAD index and higher N content in the leaves than cv. Amanda (p < 0.05). Yield of extra fruits was 15.39 t ha-1, with bio-fertilizer dose of 110 m3 ha-1 for the two cultivars. As for commercial yield, cv. Rubia was more productive (21.45 t ha-1) than Amanda (17.22 t ha-1). It was concluded that the application of swine bio-fertilizer provides to plants an adequate nutritional state and yield potential; thus, it can be recommended for non conventional fertilization for the cultivation of yellow and red pepper plants under field conditions.

Parida S.,Electroceramics Laboratory | Rout S.K.,Electroceramics Laboratory | Cavalcante L.S.,São Paulo State University | Simoes A.Z.,São Paulo State University | And 5 more authors.
Materials Chemistry and Physics | Year: 2013

In this paper, Ba(ZrxTi1-x)O3 powders with different (x) compositions were synthesized by the solid state reaction method and their structure and improvement of photoluminescence (PL) properties with the Ti substitution by Zr were discussed. The structural investigation of these powders was performed by means of X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman) spectroscopy. Their optical properties were monitored by ultraviolet-visible (UV-vis) absorption spectroscopy and PL measurements. XRD patterns indicated that the powders with x = 0 and 0.1 have a tetragonal structure while compositions with x ≥ 0.2 exhibit cubic structure. FT-Raman spectra revealed that the replacement of Ti by Zr significantly reduced the intensity of the Raman active modes. This behavior is related to the increase of undistorted [ZrO6] clusters in the global matrix at short range and decrease in local concentration of distorted octahedral [TiO6] clusters. UV-vis absorption spectra shown the presence of intermediary energy levels between the valence band (VB) and the conduction band (BC). These intermediary electronic levels are mainly related to 2p orbitals of O atoms, 4d orbitals of Zr atoms and 3d orbitals of Ti atoms between the VB and CB. A significant improvement in PL properties of Ba(ZrxTi 1-x)O3 powders was observed with an increase of undistorted [ZrO6] clusters in the lattice. Finally, we propose possible wideband models based on intermediary energy deep and shallow levels to explain the PL behavior at room temperature. © 2013 Elsevier B.V. All rights reserved.

Nogueira I.C.,Federal University of Santa Catarina | Cavalcante L.S.,São Paulo State University | Pereira P.F.S.,Federal University of Santa Catarina | De Jesus M.M.,Federal University of Maranhão | And 4 more authors.
Journal of Applied Crystallography | Year: 2013

In this article, the structural refinement, morphology and optical properties of barium strontium molybdate [(Ba1-x Sr x )MoO4 with x = 0, 0.25, 0.50, 0.75 and 1] crystals, synthesized by the co-precipitation (drop-by-drop) method, are reported. The crystals obtained were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, and Fourier transform-Raman (FT-Raman) and Fourier transform-infrared (FT-IR) spectroscopies. The shapes of the crystals were observed by means of field-emission scanning electron microscopy (FE-SEM). The optical properties were investigated using ultraviolet-visible (UV-Vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns, Rietveld refinement, and FT-Raman and FT-IR spectra showed that all of the crystals are monophasic with a scheelite-type tetragonal structure. The refined lattice parameters and atomic positions were employed to model the [BaO8], [SrO8] and [MoO4] clusters in the tetragonal lattices. The FE-SEM images indicate that increased x content produces a decrease in the crystal size and modifications in the crystal shape. UV-Vis spectra indicated a decrease in the optical band gap with an increase in x in the (Ba1-x Sr x )MoO4 crystals. Finally, a decrease in the intensity of PL emission is apparent with an increase in x up to 0.75 in the (Ba1-x Sr x )MoO4 crystal lattice when excited by a wavelength of 350nm, probably associated with the degree of structural order-disorder. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

Parija B.,National Institute of Technology Rourkela | Rout S.K.,BIT | Cavalcante L.S.,São Paulo State University | Simoes A.Z.,São Paulo State University | And 3 more authors.
Applied Physics A: Materials Science and Processing | Year: 2012

In this paper, lead-free 100-x(Bi0.5Na0.5)TiO 3-x[SrTiO3] composites ceramics with (0 ≤ x ≤ 9) were synthesized by the solid-state reaction method. Their structure, dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction patterns, Rietveld refinement data and Raman spectra revealed that the SrTiO3 cubic structure was completely diffused into the (Bi 0.5Na0.5)TiO3 lattice with rhombohedral structure. The scanning electron microscopy images showed change in grain morphology from rectangular-like to quasi-spherical grain with increase in SrTiO3 content. The dielectric permittivity increases, the Curie temperature decreases and the peaks become broaden with raise of SrTiO 3 content. Ferroelectric and piezoelectric properties of these composites ceramics showed degenerated behavior with increase of SrTiO 3. © Springer-Verlag Berlin Heidelberg 2012.

Cavalcante L.S.,São Paulo State University | Sczancoski J.C.,São Paulo State University | Batista N.C.,UESPI | Longo E.,São Paulo State University | And 2 more authors.
Advanced Powder Technology | Year: 2013

This paper reports our initial research to obtain SrWO4 microcrystals by the injection of ions into a hot aqueous solution and their photocatalytic (PC) properties. These microcrystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform (FT)-Raman spectroscopy. The shape and average size of these SrWO 4 microcrystals were observed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In addition, we have investigated the PC activity of microcrystals for the degradation of rhodamine B (RhB) and rhodamine 6G (Rh6G) dyes. XRD patterns, Rietveld refinement data and FT-Raman spectroscopy confirmed that SrWO4 microcrystals have a scheelite-type tetragonal structure without deleterious phases. FT-Raman spectra exhibited 12 Raman-active modes in a range from 50 to 1000 cm-1. FE-SEM and TEM images suggested that the SrWO4 microcrystals (rice-like - 95%; star-, flower-, and urchin-like - 5%) were formed by means of primary/secondary nucleation events and self-assembly processes. Based on these FE-SEM/TEM images, a crystal growth mechanism was proposed and discussed in details in this work. Finally, a good PC activity was first discovered of the SrWO4 microcrystals for the degradation of RhB after 80 min and Rh6G after 50 min dyes under ultraviolet-light, respectively. © 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder.

Loading UESPI collaborators
Loading UESPI collaborators