Hydrogenation properties and crystal structures of Ti-Mn-V BCC solid solution alloys

We have proposed new hydrogen absorbing alloys of the 'Laves phase related BCC solid solution alloy', the hydrogen capacity of which reaches almost double that of conventional rare-earth based AB₅ alloys. We have reported the hydrogen absorbing properties of Ti-V-Mn, Ti-V-Cr and T-V-Mn-Cr alloys. It has been accepted that the crystal structural change of BCC hydrogen absorbing alloys is the same as that of V metal. The mono-hydride (H/M=1) of V metal has a BCT structure and the di-hydride (H/M=2) has an FCC structure. However, we recently found that the Ti-V-Mn alloy shows different behaviors in phase transformation with hydrogenation to V metal. We found three hydride phases with a BCC, a deformed FCC and an FCC structure in the Ti-V-Mn solid solution alloy-H₂ system. The deformed FCC hydride phase has not yet to our knowledge been reported. The lattice constant of the deformed FCC was 0.407 nm, one axis of which is reduced by about 4%. Its single-phase region appeared at a hydrogen content between 0.8 H/M and 1.0 H/M in absorption at 298 K. The lower plateau observed due to formation of the deformed FCC hydride phase gives an increase of effective hydrogen capacity by decreasing hydrogen remaining in the alloy in the desorption process.