High-pressure crystal structures and superconductivity of Stannane (SnH4)

There is great interest in the exploration of hydrogen-rich compounds upon strong compression where they can become superconductors. Stannane (SnH ₄ ) has been proposed to be a potential high-temperature superconductor under pressure, but its high-pressure crystal structures, fundamental for the understanding of superconductivity, remain unsolved. Using an ab initio evolutionary algorithm for crystal structure prediction, we propose the existence of two unique high-pressure metallic phases having space groups Ama 2 and P 6 ₃ / mmc , which both contain hexagonal layers of Sn atoms and semimolecular (perhydride) H ₂ units. Enthalpy calculations reveal that the Ama 2 and P 6 ₃ / mmc structures are stable at 96–180 GPa and above 180 GPa, respectively, while below 96 GPa SnH ₄ is unstable with respect to elemental decomposition. The application of the Allen-Dynes modified McMillan equation reveals high superconducting temperatures of 15–22 K for the Ama 2 phase at 120 GPa and 52–62 K for the P 6 ₃ / mmc phase at 200 GPa.