Made available in DSpace on 2014-12-17T15:42:14Z (GMT). No. of bitstreams: 1
AndreiaCL_TESE.pdf: 5308625 bytes, checksum: 13df680734f410713c3992d8e7be1c8f (MD5)
Previous issue date: 2010-12-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Orthoferrites AFeO3 (A = rare earth) are an important class of perovskite oxides that
exhibit weak ferromagnetism. These materials find numerous applications as
chemical sensors, cathodes for fuel cells and catalysis, which make them interesting
from the standpoint of science and technology. Their structural, electrical and
magnetic properties are dependent on many factors such as the preparation method,
heat treatment conditions, chemical composition and replacement of cations in sites
A and/or B. In this paper, LaFe1-xMnxO3 (0 ≤ x ≤ 1) orthoferrites-type was prepared by
Pechini method and Microwave-assisted combustion reaction in order to evaluate the
influence of synthesis route on the formation of oxide, as well as the effect of parcial
replacement of iron by manganese and heat treatment on the magnetic properties.
The precursor powders were calcined at 700?C, 900?C, 1100?C and 1300?C for 4
hours and they were characterized by the techniques: Thermogravimetric analysis
(TGA), X ray diffraction (XRD), Refinement by Rietveld method, Scanning electron
microscopy (SEM), Reduction temperature programmed (RTP) and Magnetic
hysteresis measurements performed at room temperature. According to the XRD
patterns, the formation of perovskite phase with orthorhombic structure was observed
for the systems where 0 ≤ x ≤ 0.5 and rhombohedral for x = 1. The results also
showed a decrease of lattice parameters with the parcial replacement of iron by
manganese and consequently a reduction in cell volume. The hysteresis curves
exhibited weak ferromagnetism for the systems prepared by both synthesis methods.
However, a dependence of magnetization as a function of dopant content was
observed for samples produced by Pechini method. As for the systems prepared by
combustion reaction, it was found that the secondary phases exert a strong influence
on the magnetic behavior / Ortoferritas AFeO3 (A = terra rara) constituem uma importante classe de ?xidos
perovskita que exibem ferromagnetismo fraco. Estes materiais encontram in?meras
aplica??es como sensores qu?micos, catodos para c?lulas a combust?veis e na ?rea
de cat?lise, o que os fazem interessantes do ponto de vista cient?fico e tecnol?gico.
Suas propriedades estruturais, el?tricas e magn?ticas s?o dependentes de v?rios
fatores tais como: o m?todo de prepara??o, condi??es do tratamento t?rmico,
composi??o qu?mica e substitui??o de c?tions nos s?tios A e/ou B. Neste trabalho,
ortoferritas do tipo LaFe1-xMnxO3 (0 ≤ x ≤ 1) foram preparadas pelo m?todo Pechini e
pela rea??o de combust?o assistida por microondas com a finalidade de avaliar a
influ?ncia da rota de s?ntese na forma??o do ?xido, assim como o efeito da
substitui??o parcial do ferro por mangan?s e do tratamento t?rmico nas propriedades
magn?ticas. Os p?s precursores foram calcinados a 700?C, 900?C, 1100?C e
1300?C por 4 horas e caracterizados atrav?s das t?cnicas: An?lise
termogravim?trica (TG), Difra??o de raios X (DRX), Refinamento pelo m?todo de
Rietveld, Microscopia eletr?nica de varredura (MEV), Redu??o a temperatura
programada (RTP) e Medidas de histerese magn?ticas realizadas ? temperatura
ambiente. De acordo com os difratogramas, a forma??o da fase perovskita com
estrutura ortorr?mbica foi observada para os sistemas onde 0 ≤ x ≤ 0,5 e,
rombo?drica para x = 1. Os resultados tamb?m mostraram uma diminui??o dos
par?metros de rede com a substitui??o parcial do ferro por mangan?s e,
conseq?entemente uma redu??o do volume da c?lula unit?ria. As curvas de
histerese exibiram ferromagnetismo fraco para os sistemas preparados por ambos
os m?todos de s?ntese. Entretanto, uma depend?ncia da magnetiza??o em fun??o
do teor de dopante foi observada para as amostras produzidas pelo m?todo Pechini.
J? para os sistemas preparados por rea??o de combust?o, verificou-se que as fases
secund?rias exercem forte influ?ncia no comportamento magn?tico
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/17748 |
| Date | 27 December 2010 |
| Creators | Lima, Andr?ia Cavalcante de |
| Contributors | CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Carri?o, Artur da Silva, CPF:33014419704, http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4787041Z8, Lemos, Francisco das Chagas Dantas de, CPF:19907028487, http://lattes.cnpq.br/8124102870104095, Ruiz, Juan Alberto Chavez, CPF:00744293456, http://lattes.cnpq.br/5051286289341242, Ara?jo, Jos? Humberto de, Melo, Dulce Maria de Ara?jo |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Qu?mica, UFRN, BR, F?sico-Qu?mica; Qu?mica |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
Page generated in 0.003 seconds