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Master's Dissertation
DOI
https://doi.org/10.11606/D.54.1983.tde-25052009-095853
Document
Author
Full name
Carlos Alberto de Simone
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1983
Supervisor
Committee
Mascarenhas, Yvonne Primerano (President)
Craievich, Aldo Felix
Svizzero, Darcy Pedro
Title in Portuguese
Refinamento de estruturas cristalinas por difração de raios-x pelo método de mínimos quadrados utilizando dados de amostras policristalinas.
Keywords in Portuguese
Amostras policristalinas
Difração de raios-x
Abstract in Portuguese
A estrutura da florencita foi refinada pelo método de mínimos quadrados, utilizando dados experimentais obtidos através do método de Debye-Scherrer. A coleta dos dados das intensidades integradas foi feita através da leitura do difratograma de pó por um microdensitômetro óptico automático, e empregando métodos de análise numérica para fazer a integração da função (2θ,Y), tabelada a pontos eqüidistantes. Foram observados 14 picos de difração e as reflexões que se superpunham contribuindo para as intensidades dos picos foram identificadas e suas contribuições levadas em conta através de seus fatores de multiplicidade. O refinamento foi feito com o programa POWLS (Powder Least Squares) e inicialmente foram fornecidos os parâmetros posicionais dos átomos da Goyazita, que é isomorfa com a florencita. As intensidades observadas foram corrigidas pelos fatores de Lorentz-polarização e adsorção. O índice de discordância R atingido para os 14 picos de difração observados foi de 0.097. A fórmula molecular da florencita é CeAl3(PO4)2(OH)6. O composto cristaliza no sistema hexagonal com parâmetros de rede ao=6.96Å co=16.33Å α= β = 90° γ=120° V=685.07Å3. O grupo espacial é R3m com Z=3 e densidade calculada igual a 3.67g.cm-3.
Title in English
Refinement of crystal structures by x-ray diffraction using the method of least squares and data from polycrystalline samples.
Keywords in English
Polycrystalline samples
X-ray diffraction
Abstract in English
The crystal structure of the florencita was refined by least squares using experimental data obtained with the Debye-Scherrer method. An automatic optical microdensitometer was used for the data collection from powder difractogram and numerical analysis methods for the integration of the function (2θ,Y) which is tabulated at equidistant points. 14 diffraction peaks were observed, reflections which superpose contributing to the same peak were identified and their contributions were taken in account using multiplicity factors. The program POWLS (Powder Least Squares) was used for the refinement and initially the positional parameters of the atoms of the Goyazite, which is isomorfous with the florencita were used. Intensities were corrected for the Lorentz, polarization and absorption factors. The final R factor for the 14 peaks was of 0.097. The molecular formula of the florencitais CeAl3(PO4)2(OH)6. It crystallizes in the hexagonal system, space group R3m with cell ao=6.96Å co=16.33Å α= β = 90° γ=120° V=685.07Å3.
 
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Publishing Date
2009-06-01
 
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