Determination of the Fe2+ and Fe3+ concentration in MgO

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Abstract
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+.