Hydrogenation reaction of Co₃Ti alloy under high pressure and high temperature

To synthesize a novel titanium-containing hydride, a Co₃Ti alloy with a Cu₃Au-type structure was hydrogenated at 9 GPa and 900 °C. Structural changes under high pressure were monitored via in situ synchrotron radiation x-ray diffraction at BL14B1, SPring-8. The in-situ measurement reveals that novel hydride Co₃TiH_~4 is formed at 9 GPa and 900 °C. When the sample was depressurized at room temperature, the formed hydride decomposed to (the previously reported) Co₃TiH_~1 at a pressure of ~1 GPa. Co₃TiH_~1 was recovered at ambient conditions and decomposed gradually into the Co₃Ti alloy. Co₃TiH_~4 is thermodynamically stable only at pressures above 1 GPa.