Anomalous behavior of the Ni bonding strength in some LaNi_5-xAl_xH_y compounds

The nuclear resonant photon scattering technique was utilized to investigate the Ni cohesion variation in LaNi_5-xAl_x intermetallics and some of their hydrides. The resonantly scattered intensity (RSI) of 7.646-MeV ϒ rays by ⁶²Ni was measured for 0≤x≤1.5, and was analyzed by utilizing a reference pure-Ni scatterer. The RSI drops significantly at x=0.25 and increases gradually for 0.25<x≤1.5. The investigated hydrides (0.5≤x≤1.5) exhibit higher RSI values than the corresponding unhydrided intermetallics. An apparent correlation between the Ni cohesion and hydrogen uptake is suggested to be the key for understanding the puzzling hydriding characteristics of this and other aluminum-substituted intermetallic systems.