5 documents found, page 1 of 1
Análise cristalográfica da solução sólida com estrutura tipo Tungstênio Bronze ...
Lanfredi,Silvania; Nobre,Marcos A. L.; Lima,Alan R. F.Solid solution of iron doped potassium strontium niobate with KSr2(FeNb4)O15-Δ stoichiometry was prepared by high efficiency ball milling method. Structural characterization was carried out by X-ray diffraction. Crystalline structure was analyzed by the Rietveld refinements using the FullProf software. The results showed a tetragonal system with the tetragonal tungsten bronze structure - TTB (a = 12.4631 (2) Å ...
Estudo de coprólito da bacia sedimentar do Araripe por meios de espectroscopia ...
Lima,Ricardo Jorge Cruz; Freire,Paulo de Tarso Cavalcante; Sasaki,José Marcos; Saraiva,Antonio Álamo Feitosa; Lanfredi,SilvaniaCoprolites are fossilized faeces that constitute an important source of palaeobiological informations. This paper describes the characterization of some coprolite materials originated from the Romualdo Member of the Santana Formation (Araripe Basin, south of Ceará State in Brazil) by means of two techniques: X-ray powder diffraction and Fourier transform infrared spectroscopy (FT-IR). This characterization allo...
Caracterização espectroscópica de peixe do período cretáceo (Bacia do Araripe)
Lima,Ricardo Jorge Cruz; Saraiva,Antonio Alamo Feitosa; Lanfredi,Silvania; Nobre,Marcos Augusto de Lima; Freire,Paulo de Tarso CavalcanteThe study of fossils has made considerable progress over the last years as a result of the use of new experimental techniques. This paper describes the chemical composition of a fossilized fish of the Cretaceous period, from a 100 million-year-old, material originated from the Araripe Basin (northeastern Brazil). The chemical composition of the fossilized fish was analyzed by means of X-ray powder diffraction a...
Electrical characterization by impedance spectroscopy of Zn7Sb2O12 ceramic
Nobre,Marcos A. de Lima; Lanfredi,SilvaniaImpedance spectroscopy technique was used to investigate the electric properties of Zn7Sb2O12, an electroceramic with inverse spinel type structure. The electric characterization of the Zn7Sb2O12 semiconducting ceramic was performed at temperature from 250 to 550 °C, in the frequency range from 5 Hz to 13 MHz. Zinc antimoniate phase was synthesized by the polymeric precursors method. The bulk resistance curve a...
Dielectric dispersion in Bi3Zn2Sb3O14 ceramic: a pyrochlore type phase
Lanfredi,Silvania; Nobre,Marcos A. de LimaThe electric and dielectric properties of Bi3Zn2Sb3O14 ceramic were studied by impedance spectroscopy. The measurements were performed in the frequency range 5 to 13 MHz and at temperature ranges from 25 to 700 °C. The permittivity was calculated by the variation of the imaginary part of the impedance (-Im(Z)) as function of 1/omega, where omega represents the angular frequency (2pif). The parameter epsilon = f...