Ternary Na-P-H superconductor under high pressure

Abstract

Most of the H-rich superconductors have so far been discovered to be clathrate structures. Several clathrate hydrides, including ${\mathrm{H}}_{3}\mathrm{S}$, ${\mathrm{LaH}}_{10}$, and ${\mathrm{CaH}}_{6}$, 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 ${\mathrm{NaPH}}_{6}$ and ${\mathrm{NaPH}}_{8}$ in ternary Na-P-H hydrides are found to be stable under 200 GPa. The $P\overline{6}m2$ phase of the ${\mathrm{NaPH}}_{6}$ hydride is identified as a novel ternary layered H-rich superconductor, exhibiting a high critical temperature ${T}_{c}$ of 112.2 K under 200 GPa. Our calculations indicate that the high ${T}_{c}$ of the ${\mathrm{NaPH}}_{6}$ hydride under high pressure is attributed to the high density of hydrogen $s$ states present at the Fermi level. Furthermore, a metastable $Pm\overline{3}$ phase of the clathrate ${\mathrm{NaPH}}_{6}$ hydride is uncovered under 350 GPa and displays an exceptional ${T}_{c}$ of 201.4 K. These results suggest that ternary alkali metal Na-based hydrides hold promise as high-${T}_{c}$ superconductors under high pressure and offer critical insights into the design and synthesis of novel category high-temperature superconductors.