Navegando por Autor "Lima, A. C."
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Artigo 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 Structural and magnetic characterization of LaFe1-xAlxO3 (x=0 and 0.2) orthoferrites synthesized by gelatin method(Trans Tech Publications, 2017-07) Araújo, José Humberto de; Pimentel, Patrícia Mendonça; Dutra, J. L. S.; Lima, A. C.; Bagnato, Osmar Roberto; Costa, Asenete Frutuoso; Oliveira, Rosane Maria Pessoa BetanioThe rare-earth orthoferrites (LnFeO3) are promising materials for various applications, such as chemical sensors, cathode for SOFC, catalysts, among others. In general, these oxides are synthesized at temperatures higher than 700 °C. In this work, nanocrystalline LaFe1-xAlxO3 (x=0, x=0.2) powders were synthesized by a method that uses gelatin as organic precursor and heat treated at 400, 600 and 800 °C. The structural and magnetic characterization of powders was carried out by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Morphological analysis was performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD patterns revealed the formation of orthoferrites single phase since 400°C. The powders exhibited weak ferromagnetic behavior at room temperature where the values of saturation magnetization, remanence and coercivity varied with the doping and heat treatment temperatureArtigo 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