Pressure–temperature phase diagram of Ta-H system up to 9 GPa and 600^◦ C

High-pressure hydrogenation behaviors of pure metals have not been investigated exten-sively, although intense research of hydrogenation reactions under high pressure has been conducted to find novel functional hydrides. The former provides us with valuable information for the high-pressure synthesis of novel functional hydrides. A pressure–temperature phase diagram of the Ta–H system has been determined using the in situ synchrotron radiation X-ray diffraction technique below 9 GPa and 600^◦ C in this study. At room temperature, the phase boundary obtained between distorted bcc TaH_~1 and hcp TaH_~2 was consistent with the previously reported transition pressure. The experimentally obtained Clapeyron slope can be explained via the entropy change caused by hydrogen evolution from TaH_~2.