Effect of Mn substitution on crystal structure and cyclic property of Y–Ni alloy with superlattice structure

This study investigated the crystal structure, P–C isotherm, and cyclic properties of YNi₃. We discovered that hydrogen-induced amorphization (HIA) was appeared in three cycles of P–C isotherm at 303 K, but it was not observed at 273 K. An analysis of the three cycles at 303 K revealed a 55 % decrease in hydrogen capacity as compared to the first cycle. To enhance the hydrogenation properties, Mn was substituted for Ni. X-ray Rietveld refinements on YNi_2·7Mn_0·3H_3.8 reveal that the hydride phase retains the PuNi₃-type structure of the original alloy. The values of a, c, the unit cell, the MgZn₂-type cell, and the CaCu₅-type cell expanded 5.6 %, 9.3 %, 21.9 %, 25.0 %, and 18.8 % from the original alloy. The results indicated that YNi_2·7Mn_0.3 retained 91 % of its initial hydrogen capacity after three cycles at 303 K. After 120 cycles in the cyclic test, YNi₃ and YNi_2·7Mn_0.3 retained 42 % and 90 % of their initial capacity, respectively. The XRD profile of YNi₃ after 120 absorption-desorption cycles revealed significant peak broadening. Similarly, peak broadening was also observed in the XRD profile of YNi_2·8Mn_0.2 after 120 cycles. In comparison, the XRD profile of YNi_2·7Mn_0.3 after 120 cycles remained relatively unchanged from its initial state. It was observed that YNi_2·7Mn_0.3 experienced less lattice strain during hydrogenation than YNi_2·8Mn_0.2.