Structural Diversity and Superconductivity in S-P-H Ternary Hydrides under Pressure

Evolutionary structure searches revealed a plethora of stable and low-enthalpy metastable phases in the S-P-H ternary phase diagram under pressure. A wide variety of crystalline structure types were uncovered ranging from those possessing one-dimensional chains, two-dimensional sheets based on S-H or S-P-H square lattices as well as S-H or P-H honeycombs, and cage-like structures. Some of the cage-like structures could be derived from doping the high-pressure high-temperature superconducting Im3¯ m H₃S phase with phosphorus. Most of the discovered compounds were metallic; however, those derived from Im3¯ m H₃S lattices with low levels of P-doping were predicted to possess the highest superconducting critical temperatures (T_cs). The propensity for phosphorus to assume octahedral coordination and the similar radii of sulfur and phosphorus are key to maintaining a high density of states at the Fermi level in Im3¯ m S_0.875P_0.125H₃, whose T_cwas estimated to be similar to that of H₃S at 200 GPa.