Pressure hysteresis in the TiMn_1.5V_x-H₂ (x = 0.1–0.5) system

The structural characteristics of TiMn_1.5V_x (x = 0.1–0.5) alloys and the hysteresis phenomenon in the TiMn_1.5V_x-H₂ system have been studied. The TiMn_1.5V_x alloy consists mainly of the C14 Laves phase plus some of the BCC solid solution phase, depending on x. The lattice parameters of the C14 Laves phase increase slightly as x increases from 0.1 to 0.2 but are invariant with a further increase in x up to 0.3–0.5. The pressure-composition isotherms clearly show a pressure hysteresis in the TiMn_1.5V_x-H₂ system which decreases with an increase in the x value mainly due to the equilibrium pressure change for hydride formation. The free energy loss during hydride formation is related to not only the volume expansion, but also the elastic strain in the TiMn_1.5V_x alloy itself, that is, prior to hydrogen absorption.