OBSERVATION OF 2 DIFFERENT TYPES OF STABLE [FEO4- NA+](0) CENTERS IN A SILICA GLASS/

The EPR properties of the ubiquitous iron impurity in samples of a Vyc or-type silica glass of different atmospheric sintering have been stud ied. As with the low-temperature observation of dynamic interchange be tween two configurations of the [FeO4-/Na+](0) centre, two similar sta ble iron centres of different configurations based on two different pe rmanent locations of the Na+ ion have been found. The EPR resonances o f the two centres partially overlap and exhibit g-values in the range of 4.20-4.28. Both hydrogen sintering and gamma-irradiation of the gla ss were found to decrease the intensity of the signal of each centre b y an equivalent extent. The phenomenon is rationalised by considering the possibility of chemical reduction of the iron centres in each of t he two treatment processes. (C) 1998. Published by Elsevier Science B. V. All rights reserved.