Stability and properties of the Ru–H system at high pressure

Abstract

We report on a first-principles study of the phase diagram, structures and properties of the Ru–H system in the H-rich regime over a wide range of pressures. The results show that RuH is thermodynamically stable and can coexist with RuH₃ and RuH₆ under pressure. RuH and RuH₃ stoichiometries exhibit metallic character as a result of notable band structures, while RuH₆ is a semiconductor. Strikingly, some hydrogen atoms pairwise couple into H₂ units in the RuH₆ compound. An estimation of superconducting transition temperature T_c is carried out by applying the Allen-Dynes modified McMillan equation for Fmm (RuH), Pmm (RuH₃), and Pmn (RuH₃) structures and the resulting T_c reaches 0.41, 3.57 and 1.25 K at different pressures, respectively.