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

Abstract

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 YNi2·7Mn0·3H3.8 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 YNi2·7Mn0.3 retained 91 % of its initial hydrogen capacity after three cycles at 303 K. After 120 cycles in the cyclic test, YNi3 and YNi2·7Mn0.3 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 YNi2·8Mn0.2 after 120 cycles. In comparison, the XRD profile of YNi2·7Mn0.3 after 120 cycles remained relatively unchanged from its initial state. It was observed that YNi2·7Mn0.3 experienced less lattice strain during hydrogenation than YNi2·8Mn0.2.