He holds a Bachelor's Degree in Physics from the Federal University of São Carlos (1985), a Master's Degree in Applied Physics from the Institute of Physics of São Carlos - University of São Paulo (1988) and PhD in Sciences from Universite Paris XI (Paris-Sud). Currently Associate Professor MS-5, Level A3 of the Institute of Physics of São Carlos, University of São Paulo. Has experience in the field of Physics, with emphasis in the Study of the Structure of Crystalline and Amorphous Solids Address: São Carlos, São Paulo, Brazil
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H 2... more Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H 2 O 2 followed by the addition of Pb 2+ at high pH, resulting in a reactive and amorphous precipitate with (Pb:Ti=1:1) mole ratio, which was heat treated between 400 C and 700 C. The amorphous precipitate was characterized by DSC, and all of the powders were characterized by X-ray diffraction, Raman and XAS (EXAFS and XANES) spectroscopy at the Ti K edge. A metastable, stoichiometric and cubic pyrochlore phase (Pb 2 Ti 2 O 6 , Fd3m) was identified by XRD and Raman spectroscopy up to approx. 450 C. Only tetragonal PbTiO 3 was identified at higher temperatures. XAS spectra showed that the local structure around the absorbing Ti atom of the intermediate pyrochlore phase is similar to that observed in the amorphous precursor. This fact indicates that the metastable intermediate pyrochlore (Pb 2 Ti 2 O 6) is kinetically favored to be formed because of its similarity to the amorphous precipitate, instead of the slightly different and thermodynamically favored tetragonal (PbTiO 3 , P4/mmm) perovskite structure that is only formed at higher temperatures, after the crystallization of the metastable intermediate pyrochlore.
ABSTRACT This paper presents a study of the influence of particle size on the structural and diel... more ABSTRACT This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 ± 0.08 μm and 146 ± 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at Tm as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature.
One-dimensional (1D) ZnO nanorod-like structures were successfully grown via a hydrothermal metho... more One-dimensional (1D) ZnO nanorod-like structures were successfully grown via a hydrothermal method to be used as an ozone gas sensor. X-ray diffraction measurements (XRD) and field-emission scanning electron microscopy (FE-SEM) analysis revealed a preferential growth of the nanorod-like structures along the [002] direction. Electrical resistance measurements indicated a good sensitivity to different ozone concentrations (0.06-1.19 ppm) as well as long-term stability over a 6 month period at 250 degrees C. In addition, it was observed that the nanorods had a good sensitivity to ozone at room temperature when the sensor was exposed to UV illumination. This study provides an easy and efficient way to obtain 1-D ZnO nanorods exhibiting remarkable properties for applications as ozone gas sensing materials.
In this manuscript, we report an investigation into the sensitivity of two oxidizing gases (ozone... more In this manuscript, we report an investigation into the sensitivity of two oxidizing gases (ozone and nitrogen dioxide) for nanocrystalline SrTi0.85Fe0.15O3 thin films deposited by the electron beam physical vapor deposition technique. Annealing treatment at 500 degrees C enhanced the crystallization and surface roughness of the thin film. Electrical measurements revealed that the thin film was sensitive to oxidizing gases, especially to low ozone gas levels, exhibiting a fast response time, a short recovery time as well as good reproducibility and reversibility. These findings demonstrate the great potential of the SrTi0.85Fe0.15O3 compound to be applied as a selective ozone gas sensor.
In this paper, novel organic pollutants gas sensing material CuAlO2 microspheres constituted of n... more In this paper, novel organic pollutants gas sensing material CuAlO2 microspheres constituted of nanopartides were successfully prepared by wet chemical route and characterized by structural (XRD, XAS), morphological (SEM, TEM, HRTEM) and thermal (TG) analysis. In addition, the oxidation (O-3 and NO2) and reduction (NH3 and CO) toxic gas sensing properties of the prepared CuAlO2 microspheres were systematically investigated. CuAlO2 microspheres exhibited real-time response for very low detection level of 200 ppb at 200 degrees C, with fast response (29 s), recovery (45 s) time, good reproducibility and stability to ozone gas indicating their promising application in toxic gas sensor which is better than other oxidation and reduction gases. Also comparative studies of charge-transport properties mainly ascribed to the increased proportion of ozone gas exposed surface active layers are discussed in gas sensing mechanism. (C) 2015 Elsevier B.V. All rights reserved.
Extended X-ray absorption fine spectroscopy (EXAFS) and Raman scattering studies of InF3-BaF2 and... more Extended X-ray absorption fine spectroscopy (EXAFS) and Raman scattering studies of InF3-BaF2 and InFa-SrF2 binary glasses are reported. For all compositions, the local structure of the glasses is built with InF6 units. For all glasses studied, the indium neighbour's number and the In-F mean bond length are equal to the values of the InFa crystalline phase (6 and 0.205 nm, respectively).
The local order of ionic (Ag2X)y(AS2X3) 1 _y glasses (X = Se or S) has been studied in a wide com... more The local order of ionic (Ag2X)y(AS2X3) 1 _y glasses (X = Se or S) has been studied in a wide composition range using X-ray absorption fine structure spectroscopy; The silver atoms remain in a well defined chalcogenide atom surroundings made of two bonded atoms (RAs_Se = 2.58 A, Ras_ s = 2.46 A). No significant differences between sulphide and selenide glasses were observed.
We have examined the local structure of the As~Sei x (0.20-< x-< 0.57) system by Extended X-Ray A... more We have examined the local structure of the As~Sei x (0.20-< x-< 0.57) system by Extended X-Ray Absorption Fine Structure (EXAFS) measurements. The two atoms have been successively excited, with both showing a unique contribution for their radial distribution function. At the arsenic K edge, the one shell fit is consistent with the presence of pyramidal AsSe 3 building units, bridged by selenium atoms, as indicated by the data analyzed at the selenium K edge. The evolution of the Debye-Waller factor at the arsenic K edge is discussed as well as the variation of the SeAs distance observed at the selenium edge, both phenomena depending on the arsenic composition. These effects can be explained by the existence of some As-As and Se-Se homopolar bonds in the arsenic-and selenium-rich glasses, respectively. The Fourier transform magnitude from the data collected at 35 K at the arsenic K edge does not show other shells than the first As-Se principal peak. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation.
X-ray absorption spectroscopy (EXAFS and XANI~S) was used to determine the local structure of Ag-... more X-ray absorption spectroscopy (EXAFS and XANI~S) was used to determine the local structure of Ag-As-Se glasses that belong to the (Ag2Se)x(AsSe) l_x line of the phase diagram. Each of the three atoms has been excited. At the arsenic K edge, the one-shell fit shows the existence of AsSe 3 units for all compositions and an invariant Debye-Waller factor when silver content increases. At the selenium K edge, the fit shows that the total number of first neighbours around the selenium atom varies from nearly three (as in the Ag3AsSe 3 crystalline compound) for the silver-enriched glass (x = 0.43) to two (as in the As4Se 4 glass or crystalline phase) for the silver-poor glasses. The radial distribution function .for the silver K edge at room temperature shows a unique contribution related to the Ag-Se pairs. However, at low temperature (35 K) a second peak appears. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation. Based on these results a tentative model is given.
We report the results of structural studies by means of Eu s+ fluorescence line narrowing techniq... more We report the results of structural studies by means of Eu s+ fluorescence line narrowing techniques in the binary systems PbF2-GeO2 and PbF2-SiO2. Several features characteristic of the europium fluorescence in lead glasses are put forward. The absence of selectively excited emission at room temperature demonstrates an unusually large homogeneous broadening of the electronic levels. A relative increase in the 5D o ~ 7F~ (magnetic dipole) with respect to the 6D 0-, 7F2 (electric dipole) transition is observed with time-resolved detection. This effect shows that accidental coincidences of 5Do-, 7F0 energies and ~F1 splitting do occur between europium sites differing only by their 5Do lifetimes and magnetic dipole: electric dipolar relative intensities. The general characteristics are interpreted with oxygen neighbours for Eu 3÷ rather than fluorine ions. The crystal field strength expressed as Nvffi[~ (Bqk)2X47r/(2k+1)] l/z 0imited to k=2 parameters) is slightly higher in the germanate than in the silicate matrix.
A structural study of CuO supported on a CeO 2 –TiO 2 system was undertaken using X-ray diffracti... more A structural study of CuO supported on a CeO 2 –TiO 2 system was undertaken using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The results of XRD revealed the presence of only two phases, TiO 2 anatase and CeO 2 cerianite. A trend towards smaller TiO 2 crystallites was observed when cerium content increased. When the amount of cerium increased, Ti K-edge XANES analysis showed an increasing distortion of Ti sites. The results of Ce L III-edge EXAFS showed that Ce atoms are coordinated by eight oxygen atoms at 2.32 Å. For the sample containing a small amount of cerium, the EXAFS analysis indicated that the local structure around Ce atoms was highly distorted. The catalysts presented quite different Cu K-edge XANES spectra compared to the spectra of the CuO and Cu 2 O reference compounds. The Cu–O mean bond length was close to that of the CuO and the Cu atoms in the catalysts are surrounded by approximately four oxygen atoms in their first shell. Copper supported on the ceria-modified titania support catalysts displayed a better performance in the methanol dehydrogenation when compared to copper supported only on titania or on ceria.
ABSTRACT The residual stress distribution that arises in the glass matrix during cooling of a par... more ABSTRACT The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na2O–32.1CaO–48.1SiO2–2.5P2O5 (mol%) bioactive glass–ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4–1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing&#39;s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing&#39;s model.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H 2... more Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H 2 O 2 followed by the addition of Pb 2+ at high pH, resulting in a reactive and amorphous precipitate with (Pb:Ti=1:1) mole ratio, which was heat treated between 400 C and 700 C. The amorphous precipitate was characterized by DSC, and all of the powders were characterized by X-ray diffraction, Raman and XAS (EXAFS and XANES) spectroscopy at the Ti K edge. A metastable, stoichiometric and cubic pyrochlore phase (Pb 2 Ti 2 O 6 , Fd3m) was identified by XRD and Raman spectroscopy up to approx. 450 C. Only tetragonal PbTiO 3 was identified at higher temperatures. XAS spectra showed that the local structure around the absorbing Ti atom of the intermediate pyrochlore phase is similar to that observed in the amorphous precursor. This fact indicates that the metastable intermediate pyrochlore (Pb 2 Ti 2 O 6) is kinetically favored to be formed because of its similarity to the amorphous precipitate, instead of the slightly different and thermodynamically favored tetragonal (PbTiO 3 , P4/mmm) perovskite structure that is only formed at higher temperatures, after the crystallization of the metastable intermediate pyrochlore.
ABSTRACT This paper presents a study of the influence of particle size on the structural and diel... more ABSTRACT This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 ± 0.08 μm and 146 ± 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at Tm as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature.
One-dimensional (1D) ZnO nanorod-like structures were successfully grown via a hydrothermal metho... more One-dimensional (1D) ZnO nanorod-like structures were successfully grown via a hydrothermal method to be used as an ozone gas sensor. X-ray diffraction measurements (XRD) and field-emission scanning electron microscopy (FE-SEM) analysis revealed a preferential growth of the nanorod-like structures along the [002] direction. Electrical resistance measurements indicated a good sensitivity to different ozone concentrations (0.06-1.19 ppm) as well as long-term stability over a 6 month period at 250 degrees C. In addition, it was observed that the nanorods had a good sensitivity to ozone at room temperature when the sensor was exposed to UV illumination. This study provides an easy and efficient way to obtain 1-D ZnO nanorods exhibiting remarkable properties for applications as ozone gas sensing materials.
In this manuscript, we report an investigation into the sensitivity of two oxidizing gases (ozone... more In this manuscript, we report an investigation into the sensitivity of two oxidizing gases (ozone and nitrogen dioxide) for nanocrystalline SrTi0.85Fe0.15O3 thin films deposited by the electron beam physical vapor deposition technique. Annealing treatment at 500 degrees C enhanced the crystallization and surface roughness of the thin film. Electrical measurements revealed that the thin film was sensitive to oxidizing gases, especially to low ozone gas levels, exhibiting a fast response time, a short recovery time as well as good reproducibility and reversibility. These findings demonstrate the great potential of the SrTi0.85Fe0.15O3 compound to be applied as a selective ozone gas sensor.
In this paper, novel organic pollutants gas sensing material CuAlO2 microspheres constituted of n... more In this paper, novel organic pollutants gas sensing material CuAlO2 microspheres constituted of nanopartides were successfully prepared by wet chemical route and characterized by structural (XRD, XAS), morphological (SEM, TEM, HRTEM) and thermal (TG) analysis. In addition, the oxidation (O-3 and NO2) and reduction (NH3 and CO) toxic gas sensing properties of the prepared CuAlO2 microspheres were systematically investigated. CuAlO2 microspheres exhibited real-time response for very low detection level of 200 ppb at 200 degrees C, with fast response (29 s), recovery (45 s) time, good reproducibility and stability to ozone gas indicating their promising application in toxic gas sensor which is better than other oxidation and reduction gases. Also comparative studies of charge-transport properties mainly ascribed to the increased proportion of ozone gas exposed surface active layers are discussed in gas sensing mechanism. (C) 2015 Elsevier B.V. All rights reserved.
Extended X-ray absorption fine spectroscopy (EXAFS) and Raman scattering studies of InF3-BaF2 and... more Extended X-ray absorption fine spectroscopy (EXAFS) and Raman scattering studies of InF3-BaF2 and InFa-SrF2 binary glasses are reported. For all compositions, the local structure of the glasses is built with InF6 units. For all glasses studied, the indium neighbour's number and the In-F mean bond length are equal to the values of the InFa crystalline phase (6 and 0.205 nm, respectively).
The local order of ionic (Ag2X)y(AS2X3) 1 _y glasses (X = Se or S) has been studied in a wide com... more The local order of ionic (Ag2X)y(AS2X3) 1 _y glasses (X = Se or S) has been studied in a wide composition range using X-ray absorption fine structure spectroscopy; The silver atoms remain in a well defined chalcogenide atom surroundings made of two bonded atoms (RAs_Se = 2.58 A, Ras_ s = 2.46 A). No significant differences between sulphide and selenide glasses were observed.
We have examined the local structure of the As~Sei x (0.20-< x-< 0.57) system by Extended X-Ray A... more We have examined the local structure of the As~Sei x (0.20-< x-< 0.57) system by Extended X-Ray Absorption Fine Structure (EXAFS) measurements. The two atoms have been successively excited, with both showing a unique contribution for their radial distribution function. At the arsenic K edge, the one shell fit is consistent with the presence of pyramidal AsSe 3 building units, bridged by selenium atoms, as indicated by the data analyzed at the selenium K edge. The evolution of the Debye-Waller factor at the arsenic K edge is discussed as well as the variation of the SeAs distance observed at the selenium edge, both phenomena depending on the arsenic composition. These effects can be explained by the existence of some As-As and Se-Se homopolar bonds in the arsenic-and selenium-rich glasses, respectively. The Fourier transform magnitude from the data collected at 35 K at the arsenic K edge does not show other shells than the first As-Se principal peak. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation.
X-ray absorption spectroscopy (EXAFS and XANI~S) was used to determine the local structure of Ag-... more X-ray absorption spectroscopy (EXAFS and XANI~S) was used to determine the local structure of Ag-As-Se glasses that belong to the (Ag2Se)x(AsSe) l_x line of the phase diagram. Each of the three atoms has been excited. At the arsenic K edge, the one-shell fit shows the existence of AsSe 3 units for all compositions and an invariant Debye-Waller factor when silver content increases. At the selenium K edge, the fit shows that the total number of first neighbours around the selenium atom varies from nearly three (as in the Ag3AsSe 3 crystalline compound) for the silver-enriched glass (x = 0.43) to two (as in the As4Se 4 glass or crystalline phase) for the silver-poor glasses. The radial distribution function .for the silver K edge at room temperature shows a unique contribution related to the Ag-Se pairs. However, at low temperature (35 K) a second peak appears. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation. Based on these results a tentative model is given.
We report the results of structural studies by means of Eu s+ fluorescence line narrowing techniq... more We report the results of structural studies by means of Eu s+ fluorescence line narrowing techniques in the binary systems PbF2-GeO2 and PbF2-SiO2. Several features characteristic of the europium fluorescence in lead glasses are put forward. The absence of selectively excited emission at room temperature demonstrates an unusually large homogeneous broadening of the electronic levels. A relative increase in the 5D o ~ 7F~ (magnetic dipole) with respect to the 6D 0-, 7F2 (electric dipole) transition is observed with time-resolved detection. This effect shows that accidental coincidences of 5Do-, 7F0 energies and ~F1 splitting do occur between europium sites differing only by their 5Do lifetimes and magnetic dipole: electric dipolar relative intensities. The general characteristics are interpreted with oxygen neighbours for Eu 3÷ rather than fluorine ions. The crystal field strength expressed as Nvffi[~ (Bqk)2X47r/(2k+1)] l/z 0imited to k=2 parameters) is slightly higher in the germanate than in the silicate matrix.
A structural study of CuO supported on a CeO 2 –TiO 2 system was undertaken using X-ray diffracti... more A structural study of CuO supported on a CeO 2 –TiO 2 system was undertaken using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The results of XRD revealed the presence of only two phases, TiO 2 anatase and CeO 2 cerianite. A trend towards smaller TiO 2 crystallites was observed when cerium content increased. When the amount of cerium increased, Ti K-edge XANES analysis showed an increasing distortion of Ti sites. The results of Ce L III-edge EXAFS showed that Ce atoms are coordinated by eight oxygen atoms at 2.32 Å. For the sample containing a small amount of cerium, the EXAFS analysis indicated that the local structure around Ce atoms was highly distorted. The catalysts presented quite different Cu K-edge XANES spectra compared to the spectra of the CuO and Cu 2 O reference compounds. The Cu–O mean bond length was close to that of the CuO and the Cu atoms in the catalysts are surrounded by approximately four oxygen atoms in their first shell. Copper supported on the ceria-modified titania support catalysts displayed a better performance in the methanol dehydrogenation when compared to copper supported only on titania or on ceria.
ABSTRACT The residual stress distribution that arises in the glass matrix during cooling of a par... more ABSTRACT The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na2O–32.1CaO–48.1SiO2–2.5P2O5 (mol%) bioactive glass–ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4–1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing&#39;s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing&#39;s model.
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