Nature and thermal stability of paramagnetic defects in natural clay: a study by electron spin resonance

A natural clay of South of France is studied by electron spin resonance (ES R). Two radiation-induced defects are revealed, certainly localized in the quartz contained in clay. The first is the peroxy-center, associated with o xygen, formed by the action of an O-2(-) ion on a silicon atom to lead to S i-O-O-.. The second is the E'-center, where an electron was trapped in oxyg en vacancy to give equivalent to Si-.. The spectroscopic parameters were de termined. The thermal stability of these defects is studied by isothermal a nnealing experiments. Second order kinetics best explain the results, altho ugh more complex mechanisms must occur. The two defects have very different behaviors: the peroxy-center seems more stable at high temperature than th e E'-center, although its activation energy is much weaker. They could be b oth used for the ESR dating of old clay. (C) 2000 Elsevier Science Ltd. All rights reserved.