T-P phase diagram of the Mo–H system revisited

The T-P phase diagram of the Mo–H system studied earlier at hydrogen pressures up to 5.3 GPa and temperatures up to 1200 °C by in-situ X-ray diffraction [Y. Fukai et al. Mater. Trans. 44 (2003) 1359] is re-examined at P ≤ 6 GPa and T ≤ 800 °C using a quenching technique. The formation of the high-temperature fcc MoH hydride at T > 480–570 °C is not confirmed. Instead, the stability region of the low-temperature hcp MoH1.1 hydride is found to grow with pressure. The temperature of its boundary with the region of diluted Mo–H solutions rises with pressure and reaches 800 °C at P ≈ 5.5 GPa. •T-P diagram of the Mo–H system is re-examined at P ≤ 6 GPa and T ≤ 800 °C.•The formation of the fcc MoH hydride at T > 480–570 °C is not confirmed.•The stability region of the hcp MoH1.1 hydride is found to grow with pressure.