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Previous issue date: 2013-09-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this work, the structures of LaCoO3, La0,8Ba0,2CoO3 and La0,8Ca0,2CoO3 perovskites
were characterized as a function of temperature (LaCoO3 structure being analyzed only at
room temperature). The characterization of these materials were made by X-Ray Absorption
Spectroscopy (XAS), in the cobalt K-edge, taking into account the correlated Einstein model
X-ray absorption fine structure (EXAFS). The first part of the absorption spectrum
corresponded the X-ray absorption near edge structure (XANES) and extended X-ray
absorption fine structure (EXAFS). These materials were prepared by the combustion method.
The combustion products were calcinated at 900 0C, for 6 hours in air. Noted that the sample
LaCoO3 at room temperature and samples doped with Calcium and Barium in the temperature
range of 50 K to 298 K showed greater distortion to monoclinic symmetry with space group
I2/a. However, the sample doped with barium at the temperatures 50 K, 220 K, and 260 K
showed a slight distortion to rhombohedral symmetry with space group R-3c. The La0,8Ca0,
2CoO3 structure was few sensitive to temperature variation, showing a higher local distortion
in the octahedron and a higher local thermal disorder. These interpretations were in
agreement with the information electronic structural on the XANES region and geometric in
the EXAFS region / Neste trabalho foram investigados estruturas de perovskitas LaCoO3, La0,8Ba0,2CoO3 e
La0,8Ca0,2CoO3 em fun??o de temperatura, sendo que a estrutura LaCoO3 foi analisada apenas
em temperatura ambiente. As caracteriza??es destes materiais foram realizadas pela
espectroscopia de absor??o de raios X (XAS) na borda K do cobalto levando em considera??o
modelo de Einstein correlacionado na estrutura fina de absor??o (EXAFS). A primeira parte
do espectro de absor??o de raios X corresponde absor??o de raios X pr?xima ? borda de
absor??o (XANES) e a outra estende ? espectroscopia da estrutura fina de absor??o (EXAFS).
Estes materiais foram preparados pelo m?todo de combust?o. Os produtos obtidos da
combust?o foram tratados termicamente por 9000C por 6 horas nesses materiais. Observou
que a amostra LaCoO3 em temperatura ambiente e as amostras dopadas com C?lcio e B?rio na
faixa de temperatura entre 50 K a 298 K apresentaram uma maior distor??o com simetria
monocl?nica com grupo espacial I2/a. No entanto, a amostra dopada com B?rio nas
temperaturas 50 K, 220 K e 260 K mostrou uma leve distor??o com simetria rombo?drica
com grupo espacial R-3c. A estrutura La0,8Ca0,2CoO3 foi pouco sens?vel com a varia??o de
temperatura, apresentando uma maior distor??o local no octaedro e uma maior desordem
t?rmica local. Estas interpreta??es est?o de acordo com as informa??es estruturais eletr?nica
na regi?o XANES e geom?trica na regi?o EXAFS
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/17779 |
| Date | 09 September 2013 |
| Creators | Gomes, Washington Charles de Macedo |
| Contributors | CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Freitas, J?lio Cezar de Oliveira, CPF:00957245408, http://lattes.cnpq.br/2357217530716519, Nasar, Ricardo Silveira, CPF:02168290890, http://lattes.cnpq.br/9213856023536973, Silva, Elson Longo da, CPF:20753896834, Pimentel, Patr?cia Mendon?a, CPF:77858239449, http://lattes.cnpq.br/9303372770390061, 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 |
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