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Master's Dissertation
DOI
10.11606/D.54.1980.tde-27052014-151259
Document
Author
Full name
Dulcina Maria Pinatti Ferreira de Souza
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1980
Supervisor
Title in Portuguese
Defeitos puntiformes em cristais de NaCl: NaF: M++
Keywords in Portuguese
Cristal iônico
Defeitos puntiformes
Relaxação dielétrica
Abstract in Portuguese
Neste trabalho estudamos defeitos pontuais em cristais de NaCl + NaF contendo diversos íons divalentes e em especial o íon Pb++. As técnicas usadas foram as de I.T.C. e absorção ótica. Identificamos três novos defeitos e novos agregados de Pb++. Um modelo microscópico para os defeitos observados foi proposto. Dois dos novos picos de I.T.C. são identificados como relaxação do mesmo defeito constituído do íon divalente e um íon F- em sua proximidade. Pela primeira vez observou-se a conversão da relaxação dielétrica de um íon divalente isolado para a de uma posição perturbada. Os íons F- funcionam como armadilhas eficientes para a difusão do íon Pb++. O efeito do raio iônico sobre a relaxação desses defeitos foi observado e discutido. Atribuiu-se tentativamente a um par de vacâncias ao pico de I.T.C. de mais baixa temperatura
Title in English
Point Defects in NaCl : NaF : M++ crystals
Keywords in English
Dielectric relaxation
Ionic crystal
Point defects
Abstract in English
This work report results on the study of point defects in NaCl + NaF single crystals doped with several divalent ions and with more details for Pb++ ions. I.T.C. and u.v. spectroscopy were the used techniques. Three new relaxation peaks were found as well as large aggregates of Pb++ and F- ions. A microscopic model for the observed defects is proposed. Two of the new I.T.C. peaks called B and C, are identified as dielectrics relaxation of one defect - its transverse and the longitudinal relaxation modes. This defect is made of one divalent ion one F anion as its close neighbor and one vacancy. For the first time it was observed the conversion of a Pb++ ion from a normal to a perturbed lattice site. The F anions are efficient traps for divalent ion diffusion. The effect of divalent ion radius on the dielectric relaxation of these perturbed defects was observed and discussed. The lower temperature peak is tentatively attributed to relaxation of a divacancy - a pair of positive and negative vacancy bound together
 
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DulcinaMPinattiM.pdf (2.65 Mbytes)
Publishing Date
2014-05-28
 
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