Ternary Na-P-H superconductor under high pressure

Most of the H-rich superconductors have so far been discovered to be clathrate structures. Several clathrate hydrides, including H3S, LaH10, and CaH6, were predicted to be excellent superconductors through structural searches and were later confirmed through experimental synthesis. Here, we conduct extensive crystal structure searches and first-principles calculations for ternary Na-P-H hydrides under high pressure. Two stoichiometries of NaPH6 and NaPH8 in ternary Na-P-H hydrides are found to be stable under 200 GPa. The P6¯m2 phase of the NaPH6 hydride is identified as a novel ternary layered H-rich superconductor, exhibiting a high critical temperature Tc of 112.2 K under 200 GPa. Our calculations indicate that the high Tc of the NaPH6 hydride under high pressure is attributed to the high density of hydrogen s states present at the Fermi level. Furthermore, a metastable Pm3¯ phase of the clathrate NaPH6 hydride is uncovered under 350 GPa and displays an exceptional Tc of 201.4 K. These results suggest that ternary alkali metal Na-based hydrides hold promise as high-Tc superconductors under high pressure and offer critical insights into the design and synthesis of novel category high-temperature superconductors.