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Nogueira I.C.,Federal University of Santa Catarina | Cavalcante L.S.,Sao Paulo State University | Pereira P.F.S.,Federal University of Santa Catarina | De Jesus M.M.,Federal University of Maranhao | 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.

Cavalcante L.S.,Sao Paulo State University | Sczancoski J.C.,Sao Paulo State University | Batista N.C.,UESPI | Longo E.,Sao 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.

Parida S.,Electroceramics Laboratory | Rout S.K.,Electroceramics Laboratory | Cavalcante L.S.,Sao Paulo State University | Simoes A.Z.,Sao 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.

Parija B.,National Institute of Technology Rourkela | Rout S.K.,BIT | Cavalcante L.S.,Sao Paulo State University | Simoes A.Z.,Sao 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.

Goncalves R.F.,Federal University of Sao Paulo | Cavalcante L.S.,UESPI | Nogueira I.C.,Federal University of Maranhao | Longo E.,Sao 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.

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