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398 results on '"Leite, E.R."'

15. Effect of atmosphere and dopants on sintering of SnO2

Author

Varela J.A., Perazolli L.A., Longo E., Leite E.R., and Cerri J.A.

Subjects
tin oxide, sintering, dopants, sintering atmosphere, Chemical technology, TP1-1185
Abstract

Tin oxide is an n type semiconductor material with a high covalent behavior. Mass transport in this oxide depends on the surface state promoted by atmosphere or by the solid solution of aliovalent oxide doping. The sintering and grain growth of this type of oxide powder is then controlled by atmosphere and by extrinsic oxygen vacancy formation. For pure SnO2 powder the surface state depends only on the interaction of atmosphere molecules with the SnO2 surface. Inert atmosphere like argon or helium promotes oxygen vacancy formation at the surface due to reduction of SnO2 to SnO at the surface and liberation of oxygen molecules forming oxygen vacancies. As a consequence surface diffusion is enhanced leading to grain coarsening but no densification. Oxygen atmosphere inhibits SnO2 reduction by decreasing the surface oxygen vacancy concentration. Addition of dopants with lower valence at the sintering temperature creates extrinsic charged oxygen vacancies that promote mass transport at the grain boundary leading to densification and grain growth of this polycrystalline oxide.

Published
2002
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18. TiO2 thin film growth using the MOCVD method

Author

Bernardi M.I.B., Lee E.J.H., Lisboa-Filho P.N., Leite E.R., Longo E., and Varela J.A

Subjects
thin films, TiO2, MOCVD, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

Titanium oxide (TiO2) thin films were obtained using the MOCVD method. In this report we discuss the properties of a film, produced using a ordinary deposition apparatus, as a function of the deposition time, with constant deposition temperature (90 °C), oxygen flow (7,0 L/min) and substrate temperature (400 °C). The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and visible and ultra-violet region spectroscopy (UV-Vis). The films deposited on Si (100) substrates showed the anatase polycrystalline phase, while the films grown on glass substrates showed no crystallinity. Film thickness increased with deposition time as expected, while the transmittance varied from 72 to 91% and the refractive index remained close to 2.6.

Published
2001

26. Structural order-disorder transformations monitored by X-ray diffraction and photoluminescence

Author

Lima, R.C., Paris, E.C., Leite, E.R., Espinosa, J.W.M., Souza, A.G., and Longo, E.

Subjects
Photoluminescence -- Analysis, X-rays -- Diffraction, X-rays -- Usage, Chemistry, Education, Science and technology
Abstract

A study was conducted to examine the structural order-disorder transformation promoted by controlled heat treatment using X-ray diffraction technique (XRD) and photoluminescence (PL) techniques as tools to monitor the degree of structural order. The experiment was observed to be versatile and easily achieved with low cost which allowed producing distinct, but comparable results among groups.

Published
2007

34. Photoluminescence in disordered Sm-doped PbTi[O.sub.3]: Experimental and theoretical approach

Author

Lima, R.C., Espinosa, J.W.M., Gurgel, M.F.C., Paris, E.C., Leite, E.R., Joya, M.R., Pizani, P.S., Varela, J.A., and Longo, E.

Subjects
Titanates -- Optical properties, Lead compounds -- Optical properties, Samarium -- Optical properties, Semiconductor doping -- Methods, Density functionals -- Usage, Physics
Abstract

The polymeric precursor method is used to synthesize Sm-doped PbTi[O.sub.3] powder, while x-ray diffraction, photoluminescence and ultraviolet-visible are used as probes to determine the structural order degree short-, intermediate-, and long-range orders. The experimental and theoretical results have shown the presence of the localized states in the band gap, due to the symmetry break, which is responsible for visible photoluminescence at room temperature in the disordered structure.

Published
2006

45. Electrical conduction mechanism and phase transition studies using dielectric properties and Raman spectroscopy in ferroelectric Pb0.76Ca0.24TiO3 thin films

Author

Pontes, F.M., Pontes, D.S.L., Leite, E.R., Longo, E., Chiquito, A.J., Pizani, P.S., and Varela, J.A.

Subjects
Titanium -- Electric properties, Lead -- Electric properties, Dielectric films -- Electric properties, Thin films -- Electric properties, Phase transformations (Statistical physics) -- Research, Physics
Abstract

The phase transition behavior of Pb0.76Ca0.24TiO3 thin films using Raman scattering and dielectric measurement techniques is studied. The findings conclude that a Pb(sub 1-x)Ca(sub x)TiO3 (PCT)24 thin film grown by soft chemical processing exhibits a diffuse type of phase transition.

Published
2003

47. Contributor contact details

Author

Sequeira, César A.C., primary, Santos, Diogo M.F., additional, Syzdek, J.S., additional, Pawlicka, A., additional, Donoso, J.P., additional, Alloin, F., additional, Iojoiu, C., additional, de Zea Bermudez, V., additional, Silva, M.M., additional, Noto, V. Di, additional, Negro, E., additional, Lavina, S., additional, Di Noto, V., additional, Vittadello, M., additional, Abbrent, S., additional, Greenbaum, S., additional, Brandell, D., additional, Plancha, M.J.C., additional, de Freitas, J.N., additional, Benedetti, J.E., additional, Freitas, F.S., additional, Nogueira, A.F., additional, De Paoli, M.A., additional, Samui, A.B., additional, Sivaraman, P., additional, Fu, X., additional, Itoh, T., additional, Ye, L., additional, Feng, Z., additional, de Souza, F.L., additional, and Leite, E.R., additional

Published
2010
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