High pressure polyhydrides of molybdenum: A first-principles study

• The synthesized ε-MoH was demonstrated to be energetically stable up to 100 GPa.
• New Mo hydrides with stoichiometry MoH2 were predicted to be stable at high pressure.
• The phase transition sequence of MoH2 at high pressure was proposed.
• MoH and MoH2 are metallic at high pressure.

We present results from first-principles calculations on molybdenum polyhydrides under pressure. In addition to the experimental ε-phase of MoH, we find several novel structures of MoH2 and MoH3 at pressures below 100 GPa. A hexagonal structure of MoH2 becomes stable with respect to decomposition into MoH and H2 above 9 GPa, and transforms into an orthorhombic structure at 24 GPa, which remains stable up to 100 GPa. MoH3 is unstable relative to decomposition into MoH and H2 over the whole pressure range studied. Electronic structure calculations reveal that molybdenum polyhydrides are metallic under pressure.