A molecular dynamics study of grain boundary diffusion in MgO

摘要: Abstract Molecular dynamics simulations are carried out on polycystalline periclase (MgO) to determine the structure and diffusivity at grain boundaries for pressures temperatures relevant Earth’s mantle. As temperature increases, boundary becomes more disordered, with ions having incomplete coordination system occupying regions of energy landscape shallower mimima. In contrast, as pressure increases ordered. The a function can be understood in terms these structural changes. At atmospheric pressure, diffusion coefficients Mg O extrapolate increasing values melt, indicating that similar those supercooled liquid. Just liquid, slows down decreasing two reasons: there is less surmount barriers, barriers larger due ordered structure. from zero diffusivities first decrease sharply, increase associated system, then gradually beyond ∼4 GPa. conditions core-mantle region (135 GPa, 3500 °C), no observed timescale ∼50 ns, thus constrained