Hydrogenation of a TiFe-based alloy at high pressures and temperatures

•The ternary TiFe0.8Mn0.2 alloy was hydrogenated at high pressure and temperature.•Hydrogenation proceeded via phase transition and formation of BCC TiFe0.8Mn0.2 hydride.•A chemical order–disorder phase-transition temperature was below that of binary TiFe alloy.•At a rough estimate, same H content in BCC hydride and γ hydride, TiFe0.8Mn0.2H1.8.

We investigated the hydrogenation of a ternary TiFe0.8Mn0.2 alloy under high pressure (up to 6.5 GPa) and at high temperature (up to 600 °C) by in situ synchrotron radiation X-ray diffraction measurements. A chemical order–disorder phase transition and the formation of body-centered cubic (BCC) hydride were observed. The phase-transition temperature was 400 °C, which is 200 °C lower than that of a binary TiFe alloy. A disproportionation reaction, which was observed for the binary TiFe alloy, did not occur at this temperature. The BCC hydride existed stably, and new hydrides were not formed after the BCC hydride became a single phase. Since the unit cell volume of the BCC hydride was almost equal to that of the γ hydride, TiFe0.8Mn0.2H1.8, under the same pressure–temperature conditions, the hydrogen content of the former was roughly estimated as the same as that of the latter (hydrogen to metal atom ratio = 0.9).