Impact of superionic transitions on stability and dehydration of mantle hydrous phases

Determine how the superionic transition—characterized by liquid-like diffusion of protons (and potentially cations) within the crystal lattice—affects the thermal stability and dehydration processes of hydrous phases in Earth’s interior, particularly under deep lower mantle and core–mantle boundary conditions.

Background

Hydrous minerals such as δ-AlOOH, pyrite-type FeO2Hx, and hydrous aluminous SiO2 can transport water deep into Earth’s mantle. At high pressures relevant to the lower mantle, hydrogen bonds in these phases symmetrize, and several of these hydrous phases undergo superionic transitions in which protons exhibit liquid-like diffusion within an otherwise crystalline lattice.

Superionic behavior influences physical properties such as electrical conductivity and elastic moduli, and in superionic H2O ice it can alter phase stability via entropic effects. Despite these observations, the specific consequences of superionicity for the thermal stability and dehydration pathways of hydrous mantle phases have not been established, motivating a need to quantify its role under deep lower mantle and core–mantle boundary conditions.