SÍNTESE E CARACTERIZAÇÃO DO SISTEMA ESPINÉLIOS CO1-XCUXFE2O4 (X = 1,0, 0,75,0,50, 0,25, 0,0) PELO MÉTODO DOS PRECURSORES POLIMÉRICOS

Detalhes bibliográficos
Ano de defesa: 2012
Autor(a) principal: Silva, Maya Dayana Penha da lattes
Orientador(a): SILVA, Fernando Carvalho lattes
Banca de defesa: Não Informado pela instituição
Tipo de documento: Dissertação
Tipo de acesso: Acesso aberto
Idioma: por
Instituição de defesa: Universidade Federal do Maranhão
Programa de Pós-Graduação: PROGRAMA DE PÓS-GRADUAÇÃO EM QUÍMICA/CCET
Departamento: QUIMICA
País: BR
Palavras-chave em Português:
Palavras-chave em Inglês:
Área do conhecimento CNPq:
Link de acesso: http://tedebc.ufma.br:8080/jspui/handle/tede/938
Resumo: Ferrites are complex oxides, thermally stable, that presents crystalline structures equivalent to the spinel mineral.These solids alsoretain significant dielectric, magneticand catalytic properties. Thus, this work aims to obtain Co1-xCuxFe2O4spinel nanoparticles (x = 0.00, 0.25, 0.50, 0.75, 1.00) by the polymeric precursor method as well as evaluates the effect of its thermal treatment (700 - 1200 °C) over the crystalline structure. Therefore, all spinel structures were characterized by means of Raman and infrared vibrational spectroscopies and X-ray powder diffraction (XRPD). According to the X-ray diffraction patters, all the primary CoFe2O4 adopts an ideal inverse spinel structure [(Fd3 ̅m (O_h^7))], whereas the CuFe2O4 materials preferentially assume tetragonal distorted spinel structure [(I41/amd(D_4h^19))], except the 700 and 800 oC annealed CuFe2O4, that was indeed hematite. Besides, such case the FWHM analysis has indicates that the ternary thermal treatment leads to a higher organization of the lattice, as well as, increases the crystallite sizes. In general, the average crystallite sizes for CuFe2O4 varies between 27 35 nm; whereas, for the CoFe2O4 and Co-substituted CuF2O4 are respectively 28 37 nm and 33.3 52.6 nm. The crystal microdeformation oscillates between 0.17 and 0.32%, reducing, in most cases, with the thermal evolution. Raman spectra for CuFe2O4 samples shows vibrational modes at about 166 (F2g), 456 (F2g), 519 (F2g), 217 (Eg), e 686(A1g) cm-1. In other hand, CoFe2O4 samples present vibrational modes at 195, 457 and 587 cm-1 (all F2g symmetries), 298 cm-1 (A1g) and 671 cm-1(Eg). Similar optical-active modes were detected for the Co-substituted ferrites. Conversely, FTIR spectra for all CuFe2O4 shows characteristic stretching at about 531.79 559.45 cm-1 (Fe-O)A, 605.18 672.12 cm-1 (Cu-O)Aand 474.69 397.33 cm-1 (Fe-O)B. However, the CoFe2O4 samples exhibits strong stretching modes at 581.70 578.51 cm-1 (Co-O)A. Similar modes were also observed for the intermediary ferrites. Finally, the UV-vis spectra for CuFe2O4 shows 6A1g → 4Eg (G) (Fe3+ )B, and 6A1g → 4Eg (G) (Cu2+)Atransitions between 2.14 2.72 eV and 1.76 1.80 eV, respectively. However, the CoFe2O4 ferrites presents6A_1g → 2A_2g(P)(Co2+)A electronic transitions 2.11 and 2.39 eV.