The oxidation/reduction behavior of iron in the Sr[Ti1 - Fe-y(y)]O-x solid-solution system, for y is an element of [0.002: 0.05], under various oxygen partial pressures was examined through the use of electron paramagnetic resonance (EPR) spectroscopy. The results indicate that iron has been induced to move between di- tri- and tetravalent oxidation states. This results with the centers functioning as either a source (oxidation) or as a sink (reduction) for electrons. In particular it is shown that the reducibility of iron decreases with increasing iron content. (C) 2010 Elsevier B.V. All rights reserved.