43 / 2023-04-07 15:43:39

Silica-water superstructure and one-dimensional superionic conduit in Earth’s mantle

high dimensional neuro-network potential, nominally anhydrous minerals

高压物理与材料科学 > 高压地球科学-I

Water in Earth’s deep interior is predicted to be hydroxyl (OH^-) stored in nominally anhydrous minerals (NAMs), profoundly modulating both structure and dynamics of Earth’s mantle. Here, we employ a high dimensional neuro-network potential and machine-learning algorithm to investigate the weight percent water incorporation in stishovite, a main constituent of the subducted oceanic crust. We found stishovite and water prefer forming medium- to long-range ordered superstructures, featuring one-dimensional water channels. Synthesizing single-crystals of hydrous stishovite, we verified the ordering of OH^- groups in the water channels through optical and nuclear magnetic resonance spectroscopy; and found an average H-H distance of 2.05(3) Å, confirming our simulations. Upon heating, H-atoms were predicted to behave fluid-like inside the channels, leading to an exotic 1D superionic state. Thus water-bearing stishovite could feature high ionic mobility and strong electrical anisotropy, manifesting as electrical heterogeneity in Earth’s mantle.