Formação e estabilização de ε-Fe2O3 precipitado em nanoheteroestruturas de α-(Cr,Fe)2O3 por uma estratégia de dopante-quelação

• Ano de defesa: 2021
• Autor(a) principal: Attah-Baah, John Matthias
• Orientador(a): Ferreira, Nilson dos Santos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Programa de Pós-Graduação: Pós-Graduação em Física
• Palavras-chave em Português: Nanopartículas de óxido de cromo; Óxido de ferro; Sol-gel; Difração de raios X (DRX); Refinamento Rietveld (RR); Espectroscopia Mӧssbauer; Espectros Raman; Espectroscopia de infravermelho com transformada de Fourier
• Palavras-chave em Inglês: Nanoparticles chromium oxide; Iron oxide; Doping; X-ray diffraction (DRX); Rietveld refinement (RR); Mӧssbauer spectroscopy; Raman spectra; Fourier transform infrared spectroscopy.
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://ri.ufs.br/jspui/handle/riufs/16327

A sequence of α-Cr2−xFexO3 (x =0.0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; and 1.0) nanoparticles have successfully been synthesized by sol-gel method at a calcination temperature of 500ºC, using Cr(NO3)3∙9H2O (99.9% purity), Fe(NO3)3·9H2O (99.9% purity), as precursor material and D-glucose as substrate. X-ray diffraction (DRX) patterns, Rietveld Refinement (RR), 57Fe Mӧssbauer Effect spectroscopy (ME), Raman spectroscopy, and Fourier Transform Infrared spectroscopy (FT-IR) were employed to study the structural characterization, qualitative phase analysis, magnetic ordering effects, structural vibrational phenomenon, and the chemical functional behavior of the as-synthesized nanoparticles. From the DRX patterns and X´Pert Pro 3 software analysis, the chromium oxide was found to crystallize in the rhombohedral structure of the corundum (Al2O3) type belonging to the R3̅c(D3 6d) space group. The qualitative phase analysis was performed by Rietveld refinement using the “Fullprof” program of α-Cr2−xFexO3, where the average crystallite sizes were estimated by the DebyeScherer´s formula to be 12.1 ± 1.3nm ≤ x ≤ 40.5 ± 63.1nm. Increasing Fe2O3 content was identified with different phases (stable α phase, ε metastable polymorph of Fe2O3, and CrFe– alloy phases) in the DRX patterns, while Cr2O3 always remains in the eskoliate phase. The effect of particle size on the crystal lattice distortion, unit-cell volume, and lattice strain is discussed. The observed isomer shift (IS) values from 57Fe Mӧssbauer spectra analysis undoubtedly depicts the successful replacement of Fe3+ ions for the main Cr3+ ion sites, illustrating strong superparamagnetic phenomenon for all α-Cr2−xFexO3 hematite; while weak ferromagnetic ordering for α-Cr2−xFexO3(x>0.3) hematite was observed. Thus, in the α-Fe2O3 (x>0.3) patterns, the larger hyperfine field Hint ~ 50.24 – 51.71T can be ascribed with Fe3+ ions which are not influenced by the presence of Cr, while in α-Cr2-xFexO3 (x>0.3) the smaller hyperfine field Hint ~ 47.98 – 48.34T can be associated Fe3+ ions that have Cr3+ ions in close proximity.The Raman vibrational modes were observed for all α-Cr2−xFexO3 samples, most importantly, the spectral reveal five Raman active modes for x = 0.3 i.e. 2A1g and 3Eg at 674, 541, 610, 749, and 504cm-1, with one magnon mode at 841cm-1, respectively. The theoretically forbidden band at ~666cm-1 was observed as a result of IR active mode Eu(LO) or possibly induced by surface defects or stress. FT-IR spectra validated the purity, structural changes, or chemical bonding of Cr2O3 and doped nanoparticle.