Al-O--Al paramagnetic defects in kaolinite |
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Authors: | Blandine Clozel Jean-Marie Gaite Jean-Pierre Muller |
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Institution: | 1. Laboratoire de Minéralogie-Cristallographie, URA CNRS 09, IPGP and Universités de Paris 6 et 7, 4, Place Jussieu, F-75252, 05, Paris Cedex, France 3. Centre de Recherche sur la Matière Divisée, U.F.R. Faculté des Sciences, Université d'Orléans, rue de Chartres, B.P. 6759, 2, Orléans Cedex, France 4. O.R.S.T.O.M., Département T.O.A., UR12 “Geosciences de l'Environnement Tropical”, France
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Abstract: | Trapped holes located on Al-O-Al bonds in kaolinite were studied by electron paramagnetic resonance spectroscopy (EPR) at 9.3 and 35 GHz applied to well-crystallized, X-ray irradiated and oriented samples. The Q-band EPR spectrum is characterized by three clearly separated groups of 11 quasi-equidistant superhyperfine lines centered at gxx=2.040±0.0005, gyy=2.020±0.0005 and gzz=2.002±0.001. In each of these groups, the 11 superhyperfine lines exhibit intensities according to the ratios 12345654321. An angular dependence of the Q-band EPR spectrum with respect to the magnetic field is demonstrated by measurements on oriented films of kaolinite. An appropriate numerical treatment of the EPR spectra is described, which allowed extraction of the SuperHyperfine Structures (SHFS). X-and Q-band spectra have also been simulated. It is concluded from these experiments that only one type of center is present. This center, labelled the B-center in the literature, is very probably a hole trapped on oxygen (O- center) atoms coupled to two octahedral aluminium. |
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