Hydriding properties and crystal structure of NaCl-type mono-hydrides formed from Ti-V-Mn BCC solid solutions

摘要

Hydriding properties and crystal structure of NaCl-type mono-hydrides of Ti_xV_yMn_(3.0-x-y) (0.8<=x<=1.2, 1.0<=y<=1.3) BCC solid solutions were investigated. This system had two plateaus in the P-C isotherm between 0.001 and 5.0 MPa at 353 K. They correspond to two-phase regions: a solid solution and mono-hydride region; and a mono-hydride and di-hydride region. Absorption and desorption pressures of both plateaus changed almost linearly with the unit cell volume of the as-cast alloys. The slopes of the linear relations for the first plateau (solid solution-mono-hydride) were similar to those reported for AB_5 compounds, while the slopes for the second plateau (mono-hydride-di-hydride) were several times larger than those for the first plateau. The NaCl-type mono-hydrides studied had either a pseudo-cubic FCC or an FCC structure with an axial ratio (c'/a')=0.91-1.0. The ratio (c'/a') depended on alloy composition. Mn-rich samples formed mono-hydrides with a cubic structure ((c' /a')= 1.0) and increasing Ti fraction decreased (c'/a').