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Doctoral Thesis
DOI
10.11606/T.43.1993.tde-22062012-150022
Document
Author
Full name
Mario Ernesto Giroldo Valerio
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1993
Supervisor
Committee
Blak, Ana Regina (President)
Alves, Oswaldo Luiz
Monteiro, Waldemar Alfredo
Vieira Junior, Nilson Dias
Watanabe, Shigueo
Title in Portuguese
Agregacao de defeitos induzida pelo Al3+ Em solucões sólidas de fluoreto De cálcio com Yb3+ E La3+
Keywords in Portuguese
CaF2
Simuladores computacionais
TSDC
TSPC
Abstract in Portuguese
Apresentamos, pela primeira vez, estudos empregando Simulações Computacionais Estáticas e TSPC e TSDC de soluções sólidas de CaF2 com AIF (de 0,004 a 0,05 mol%), YbF3 e LaF? (- 0,l moi%). Os espectros de TSDC revelaram que: i) abaixo de 270K, as amostras só com Yb3+, La3+ e as multidopadas possuem a banda dos dipolos 1(0(0/11e dos defeitos 1j0/1/21, e as amostras pura ou só com A13+ não apresentam nenhuma banda; ii)acima de 270K, as amostras pura ou só com La3+ apresentam uma banda em 300K, atribuída a deslocações, e uma relaxação próxima a temperatura de polarização. As demais amostras apresentam uma banda predominante na faixa de 370 a 400K além desta última. TSPC combinado com TSDC mostrou que as bandas em 300K e entre 370 e 400K são devidas a fenômenos localizados de polarização e despolarização. Simulações computacionais mostraram que o A13+ não estabiliza dipolos isolados pois a energia de ligação dos agregados cubo-octaedrais é duas vezes menor do que a energia obtida para as terras raras. Nas soluções multidopadas, o AI3+ reduziu em mais de duas vezes a energia de ligação dos agregados cubo-octaedrais. As principais conclusões são: i)a banda entre 370 e 400K é devida ao agregado cubooctaedral; ii)o AI3+ gera preferencialmente agregados grandes do tipo cubo-octaedral; e iii)nas soluções multidopadas, o A13+ atua como "indutor" destes agregados.
Title in English
Aggregation defects induced by Al 3 + in solid solutions of calcium fluoride with Yb3 + and La3 +
Keywords in English
CaF2
computer simulators
TSDC
TSPC
Abstract in English
In the present work, we report, for the first time, measurements of TSDC and TSPC combined with Static Computer Simulation in the CaF2 solid solutions with one or more of the fluorides of aluminium (concentration range between 0.004 and 0.05 mol%), yterbium and lanthanum (concentration of about 0.1 mol%). The following behavior was found in the TSDC spectra: i) below room temperature, the Yb3+ and La3+ and the multidoped samples revealed the 1101011 1 dipole band and the 110/1/21 band while the A13+ and the pure samples displayed no bands; ii) from room temperature, the La3+ and the pure samples showed a depolarization band at 300K due to dislocations, while all the other samples exhibited a band near 370-400K. Combining TSPC and TSDC it was possible to verify that both relaxation bands are due to some kind of localized polarization fenomena. The Computer Simulation results made clear that it is improbable to find isolated A13+ dipoles since the binding energy of the cubo-octahedral cluster is more than two times lower than the values obtained for the rare earth ions. Concerning to the multidoped systems, the binding energies of the mixed cubo-octaedral clusters with A13+ and one of the rare earth ions, were less than half of the values obtained for the same cluster with the rare earth ions. The main conclusions of this work can be sumarized as follows: i) the 370-400K band is due to the cubo-octaedral cluster; ii) the A13+ gives rise mainly to cubo-octahedral clusters; and iii) inside the multidoped samples, the A13+ promotes the formation of cubo-octaedral clusters with the rare earth ions.
 
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Publishing Date
2012-06-22
 
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