• Miao, Maosheng
• Lowe, Angus
• Li, Xiaofeng
• Hermann, Andreas
• Conway, Lewis

Abstract

<jats:title>Abstract</jats:title><jats:p>Studies of molecular mixtures containing hydrogen sulfide (H<jats:sub>2</jats:sub>S) could open up new routes towards hydrogen-rich high-temperature superconductors under pressure. H<jats:sub>2</jats:sub>S and ammonia (NH<jats:sub>3</jats:sub>) form hydrogen-bonded molecular mixtures at ambient conditions, but their phase behavior and propensity towards mixing under pressure is not well understood. Here, we show stable phases in the H<jats:sub>2</jats:sub>S–NH<jats:sub>3</jats:sub> system under extreme pressure conditions to 4 Mbar from first-principles crystal structure prediction methods. We identify four stable compositions, two of which, (H<jats:sub>2</jats:sub>S) (NH<jats:sub>3</jats:sub>) and (H<jats:sub>2</jats:sub>S) (NH<jats:sub>3</jats:sub>)<jats:sub>4</jats:sub>, are stable in a sequence of structures to the Mbar regime. A re-entrant stabilization of (H<jats:sub>2</jats:sub>S) (NH<jats:sub>3</jats:sub>)<jats:sub>4</jats:sub> above 300 GPa is driven by a marked reversal of sulfur-hydrogen chemistry. Several stable phases exhibit metallic character. Electron–phonon coupling calculations predict superconducting temperatures up to 50 K, in the <jats:italic>Cmma</jats:italic> phase of (H<jats:sub>2</jats:sub>S) (NH<jats:sub>3</jats:sub>) at 150 GPa. The present findings shed light on how sulfur hydride bonding and superconductivity are affected in molecular mixtures. They also suggest a reservoir for hydrogen sulfide in the upper mantle regions of icy planets in a potentially metallic mixture, which could have implications for their magnetic field formation.</jats:p>

Topics

• impedance spectroscopy
• phase
• Hydrogen
• superconductivity
• superconductivity