Synthesis of Superconducting Cobalt Trihydride

The Co–H system has been investigated through high-pressure, high-temperature X-ray diffraction experiments combined with first-principles calculations. On compression of elemental cobalt in a hydrogen medium, we observe face-centered cubic cobalt hydride (CoH) and cobalt dihydride (CoH 2 ) above 33 GPa. Laser heating CoH 2 in a hydrogen matrix at 75 GPa to temperatures in excess of ∼800 K produces cobalt trihydride (CoH 3 ) which adopts a primitive structure. Density functional theory calculations support the stability of CoH 3 . This phase is predicted to be thermodynamically stable at pressures above 18 GPa and to be a superconductor below 23 K. Theory predicts that this phase remains dynamically stable upon decompression above 11 GPa where it has a maximum T c of 30 K.