Hydrogen Pentagraphenelike Structure Stabilized by Hafnium: A High-Temperature Conventional Superconductor

The recent discovery of H3S and LaH10 superconductors with record high superconducting transition temperatures T-c at high pressure has fueled the search for room-temperature superconductivity in the compressed superhydrides. Here we introduce a new class of high T-c hydrides with a novel structure and unusual properties. We predict the existence of an unprecedented hexagonal HfH10, with remarkably high value of T-c (around 213-234 K) at 250 GPa. As concerns the novel structure, the H ions in HfH10 are arranged in clusters to form a planar pentagraphenelike sublattice. The layered arrangement of these planar units is entirely different from the covalent sixfold cubic structure in H3S and clathratelike structure in LaH10. The Hf atom acts as a precompressor and electron donor to the hydrogen sublattice. This pentagraphenelike H-10 structure is also found in ZrH10, ScH10, and LuH10 at high pressure, each material showing a high T-c ranging from 134 to 220 K. Our study of dense superhydrides with pentagraphenelike layered structures opens the door to the exploration of a new class of high T-c superconductors.