Oxygen vacancy diffusion in davemaoite (CaSiO3 perovskite): Implications for the redox equilibrium and the electrical conductivity of Earth’s lower mantle

Davemaoite (CaSiO 3 ), a major rock-forming mineral in the Earth’s lower mantle, adopts a perovskite structure, which is known for the rapid diffusion of extrinsic oxygen vacancies (OV). Here, we use molecular dynamics simulations in conjunction with a machine learning potential to systematically investigate extrinsic OV diffusion in davemaoite at lower mantle conditions. We determine diffusion coefficients ( D v ) for a series of temperatures along isobars of 25, 50, 75, 100 and 125 GPa and find that computed diffusivities closely follow an Arrhenian behavior. The pre-exponential factor is pressure independent with log D v ∘ = -6.53 ± 0.06 and the activation enthalpy increases nonlinearly with pressure from 0.87 eV to 1.66 eV. On the basis of the Arrhenian model, we predict that D v decreases throughout the lower mantle by at least one order of magnitude along geotherms representative of the ambient mantle and subducted lithosphere. We argue that despite the high OV diffusivities, the davemaoite component of subducted oceanic crust does not achieve complete redox equilibration with the surrounding mantle on its way to the core-mantle boundary, and that significant redox exchange is limited to the upper parts of the lower mantle. Finally, we provide arguments that the electrical conductivity of most parts of the lower mantle cannot be explained by ionic conductivity and that its electrical conductivity must therefore be determined by iron-induced polaron hopping.