PHASE TRANSFORMATIONS OF THE LANI5-H2 SYSTEM

Pressure-composition isotherms have been measured for the LaNi//5-H//2 system. The isotherms at higher than 80 degree C clearly showed two plateaus on desorption, while the gap between two plateaus at the compositon LaNi//5H// approximately equals //3 was much smaller in absorption than it was in desorption. In situ X-ray diffraction measurements have been performed at 84 degree C in the pressure range up to 4. 5 MPa and a new hydride phase corresponding to LaNi//5H// approximately equals //3 was found. The lower plateau on the isotherms is ascribed to the coexisting region of alpha phase (solid-solution phase) and beta phase (LaNi//5H// approximately equals //3) and the higher plateau to that of beta phase and gamma phase (LaNi//5H//6). Changes in lattice parameters have also been measured along these phase transformations.