High-pressure polymorphism of FeO? An alternative interpretation and its implications for the Earth's core

Abstract

It has been reported that no stoichiometric FeO can be formed at temperatures above about 600°C regardless of pressure. The stoichiometry of FeXO quenched from static high pressure and temperature experiments appears to decrease with increasing pressure in the range 100–300 kbar. On the basis of these observations, we have re-interpreted the recent shock results on Fe0.94O, and have found that the Hugoniot data can be reasonable interpreted by the same shift in stoichiometry as observed in the static high-pressure experiments instead of a first-order transformation as proposed. If oxygen is assumed to be the light component of the outer core, the outer core can be chemically homogeneous only if the stoichiometry of FeXO decreases with increasing pressure. A constant stoichiometry would demand that the oxygen content decreases by a factor of 2 from the top to the bottom of the outer core. A chemically homogeneous outer core is consistent with a convecting outer core.