Estudo das propriedades estruturais de nanopartículas de Zn1-xCexO1-δ (0≤x≤0,15)

• Ano de defesa: 2021
• Autor(a) principal: Carvalho, Emanoel Silva
• 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: Propriedades estruturais; Nanopartículas; Óxido de zinco; Dopagem; Cério
• Palavras-chave em Inglês: Structural properties; Nanoparticles; Zinc oxide; Doping; Cerium
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://ri.ufs.br/jspui/handle/riufs/17260

In this work, the structural properties of crystalline nanoparticles of pure and doped zinc oxide with different nominal concentrations of cerium, [Zn1-xCexO1-δ (x = 0,00, 0,03, 0,06, 0,10 and 0,15)], obtained through the microwave assisted hydrothermal synthesis route, are studied. Xray diffraction measurements, refinement by the Rietveld method and Raman spectroscopy were performed. The XRD analyzes indicate that the samples have good crystallinity, with all peaks allowed for the hexagonal wurtzite type structure of the space group P63mc and point group C4 6v. It was observed non-linear displacement of the diffraction peak (100) to lower angles caused by the increase of dopant in the ZnO matrix. Increase in the relative intensity of the peak (002) due to the increase in the size of the crystallite in the direction [001] and increase in the intensity of the peak (110) associated with the conditions of production of the samples. Increasing of the full width at half maximum of the peaks due to the increase amount of defects in the material. A secondary phase was found, at first, not identified in position 2θ≈34º. The profiles observed and calculated with the Rietveld refinement are in good fit and indicate that the material has a hexagonal wurtzite structure, confirming the results of the XRD. The density of the material increases from 5,7 g/cm3 to 6,1 g/cm3, the volume of the unit cell from 47,2 Å3 to 47,8 Å3, the parameters “a” from 3,24 Å to 3,25 Å and “c” from 5,19 Å to 5,21 Å and the normalized relative height of oxygen from 0,38 to 0,40 with the increase of cerium. The c/a factor remains 1.60 for all samples. The size of the crystallite increases from 30 nm to 31 nm for the sample with 3% cerium and decreases for the other samples staying close to 25 nm. The stress decreases for samples with 3% and 6% of cerium and increases for other samples. The secondary phase could not be identified with the Rietveld refinement. Raman spectrograms have vibration modes A1(TO), E1(TO), E2(H), A1(LO) and E1(LO) characteristic of the hexagonal structure of the wurtzite type. Present E2(H)-E2(L) and A1(LO)-E2(H) modes assigned to second-order Raman processes and a mode of approximately 205 cm-1 assigned to oxygen vacancies. Another vibrational mode was identified at 452 cm-1, 465,6 cm-1 and 453,5 cm-1 for samples with cerium doping with 6%, 10% and 15% respectively, attributed to the symmetric vibration of oxygen in around the cerium atoms identified as F2g mode characteristic of the cubic structure of the fluorite type belonging to cerium oxide crystals. The existence of this mode in these samples indicates that the ZnO matrix has a solubility limit due to the non-compatibility between the cerium and zinc atoms.