It has been repeatedly suggested that an iron-rich oxide might accumulate on the Earth’score-mantle boundary by various processes. Recent studies showed that FeO with a rock salt (B1)-typestructure undergoes pressure- and temperature-induced metallization at the Earth’s lower mantle conditions.This implies similar metallization or decomposition of the lower mantle phase, (Mg,Fe)O, under highpressure-temperature conditions. We performed simultaneous X-ray diffraction and electrical conductivitymeasurements on (Mg0.20Fe0.80)O and (Mg0.05Fe0.95)O magnesiowüstites up to 140 GPa and 2100 K, andwe examined recovered samples bymeans of an analytical transmission electronmicroscope. The experimentsrevealed very high electrical conductivity of the magnesiowüstite samples and their minimal temperaturedependence above 85 GPa and 1300 K, yet the samples remained insulators. We also found decomposition of(Mg0.05Fe0.95)O into almost pure FeO and iron-rich (Mg,Fe)O due to metallization of the FeO component,while such a reaction was not observed in (Mg0.20Fe0.80)O. The observed high electrical conductivity anddecomposition of iron-rich (Mg,Fe)O magnesiowüstite could enhance the heterogeneities in the electricaland thermal conductivity at the Earth’s core-mantle boundary region.
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