Navegando por Autor "Silva, Z. R."
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Artigo Low-temperature synthesis of single-phase crystalline LaNiO3 perovskite via Pechini method(Elsevier, 2002-03) Fernandes, Joana D. G.; Melo, Dulce Maria de Araújo; Zinner, Léa Barbieri; Salustiano, Clayton de Matos; Silva, Z. R.; Martinelli, Antonio Eduardo; Nasar, Marinalva Cerqueira; Alves Júnior, Clodomiro; Silva, Elson Longo da; Bernardi, Maria Inês BassoLaNiO3 powders were prepared from polymeric precursors. The material was calcinated either under flowing oxygen or in air at temperatures ranging from 300 to 800 °C. The formation of new phases upon calcination was investigated using X-ray diffraction, thermal gravimetric analysis, Fourier-transform infrared spectroscopy and CHN analysis. The results revealed the formation of a single-phase powder having the perovskite structure at temperatures as low as 600 °C. The atmosphere did not significantly affect the final productArtigo Room temperature photoluminescence of (RE)NiO3 (RE=La, Y, Er, Ho, Nd and La1-xYx)(ABCERAM, 2007) Silva, Z. R.; Melo, Dulce Maria de Araújo; Lima, A. C.; Silva, Elson Longo da; Melo, Marcus Antônio de Freitas; Martinelli, Antonio EduardoThe nature of visible photoluminescence (PL) at room temperature in amorphous (RE)NiO3 (RE=La, Y, Er, Ho, Nd and La1-xYx) is discussed. Powders of this system were prepared by the polymeric precursor technique. The presence of broad PL band emission spectra at room temperature indicated increasing structural order with addition of rare earth elementsArtigo Room temperature photoluminescence of amorphous BaxSr1−xTiO3 doped with chromium(Elsevier, 2004-03) Melo, Dulce Maria de Araújo; César, A.; Martinelli, Antonio Eduardo; Silva, Z. R.; Leite, Edson Roberto; Silva, Elson Longo da; Pizanni, Paulo SérgioABO3 amorphous materials, such as BaTiO3 (BT), SrTiO3 (ST), PbTiO3 (PT), and BaxSr1−xTiO3 (BST) have recently attracted a good deal of attention due to their ferroelectric and electro-optical properties. Intense photoluminescence at room temperature was observed in amorphous titanate doped with chromium (BaxSr1−xTi1−yCryO3) prepared by the polymeric precursor method. Results indicated that substantial luminescence at room temperature was achieved with the addition of small Cr contents to amorphous BaxSr1−xTi1−yCryO3. Further addition of Cr or crystallization were deleterious to the intensity of the luminescent peak obtained for excitation using λ=488.0 nmArtigo Synthesis and characterization of lanthanum- and yttrium-doped Fe2O3 pigments(ABCERAM, 2007) Melo, Dulce Maria de Araújo; Melo, Marcus Antônio de Freitas; Martinelli, Antonio Eduardo; Silva, Z. R.; Cunha, Jardel Dantas da; Lima, A. C.Iron oxide has been doped with rare earth ions (yttrium or lanthanum) aiming at producing ceramic pigments with hues that vary from orange to brown. The powders were synthesized from polymeric precursors using the Pechini method and subsequently calcined between 900 and 1100 oC. The resulting pigments were characterized by BET, X ray diffraction, colorimetric analysis, UV-visible, infrared (FTIR), particle size distribution and thermal analysis. The color depicted by La/Fe powders changed as the calcination temperature increased from 900 oC to 1100 oC, as established by the corresponding changes in the values of the colorimetric coordinates from L* a* b* = 49.003, 10.541, 12.609 to L* a* b* = 31.279, 6.096, 6.877. On the other hand, Y/Fe powders were little affected by similar changes in the calcination temperature, revealing the effect of yttrium on the color stability of the powder. The values of the colorimetric coordinates in this case varied from L*a*b* = 45.230, 17.315, 28.750 to L* a* b* =51.631, 15.726, 25.825. Structural changes were also noticed as a function of the size of the rare earth ion added to the structure. Upon calcination at 900°C, lanthanum stabilized the ABO3-type perovskite structure whereas the presence of yttrium resulted in a mixture of oxides