Determination of the Fe2+ and Fe3+ concentration in MgO

Crystals of MgO containing 140 ppm iron were reduced in CO or oxidized in air at 1150 °C and the iron concentration in different valences was determined by optical and magnetic techniques. Optical density, electron spin resonance, and magnetic circular dichroism measurements gave self-consistent results that yield calibration constants for determining the Fe2+ and Fe3+ concentrations by optical means. Oscillator strengths of the absorption bands at 1000 and 285 nm were calculated from this knowledge of the iron concentration. At low concentrations more than 90% of the iron is unassociated, Fe2+ or Fe3+. Alternate oxidation and reduction converted 80% of this iron between these valence states, while the other 20% remained as Fe2+.