Superionicity of oxygen-deficient davemaoite and its impact on the deep-Earth oxidation cycle.

Davemaoite (CaSiO perovskite) is an essential mineral in Earth's lower mantle, thought to be solidified directly from an early magma ocean. Despite its abundance, the impact of defects, particularly oxygen vacancies, on davemaoite's properties under mantle conditions has not been thoroughly investigated. Here, we use machine learning molecular dynamic simulations to examine the behavior of oxygen-deficient davemaoite structures under high pressures and temperatures. Our simulations reveal its superionic transition driven by oxygen's diffusion, enhancing electrical conductivities. Our predicted phase diagrams demonstrate that higher oxygen vacancy concentrations expand the superionic phase region. This superionic behavior implies that defective davemaoite could play a critical role in early mantle oxidation and deep-Earth oxygen cycling, providing a potential major source of mobile oxygen in the deep mantle. These findings offer fresh insights into the geodynamic processes in Earth's early mantle and suggest that oxygen-deficient davemaoite could primarily contribute to the electrical conductivity and oxidation state of the deep lower mantle.