The interdiffusion of Fe and Mg was investigated experimentally under hydrous conditions. Single crystals of MgO, in contact with (Mg0.73Fe0.27)O, were annealed hydrothermally at 300MPa between 1000 and 1250C using a Ni–NiO buffer. Following electron microprobe analysis, the dependence of the interdiffusivity upon the Fe concentration was determined by using a Boltzmann–Matano analysis. For a water fugacity of 300MPa, the Fe–Mg interdiffusion coefficient in FexMg1−xO, with 0.01 ≤ x ≤ 0.25, could be described by:

D (m2/s) = 5 x 10-4x0.8exp[-(270-80x)(kJ/mol)/RT]

For x = 0.1, and at 1000C, the Fe–Mg interdiffusion was a factor of 4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion was attributed to an increased concentration of metal vacancies resulting from the incorporation of H.

Influence of Hydrogen on Fe–Mg Interdiffusion in (Mg,Fe)O and Implications for Earth’s Lower Mantle. S.Demouchy, S.J.Mackwell, D.L.Kohlstedt: Contributions to Mineralogy and Petrology, 2007, 154[3], 279-89