Hysteresis in Ce-based AB5-type metal hydrides

The effect of partial substitution of Ni in Ce1-xLaxNi5 intermetallic compound-hydrogen systems by Al, Sn and Co on hysteresis has been studied by pressure-composition-isotherm measurements. Al- and Sn-containing systems manifested a dramatic lowering of equilibrium pressures in comparison with their corresponding base compounds which can be attributed to higher Al and Sn atomic radii than that of Ni, and consequently, expanded intermetallic matrix. The addition of tin led also to widening of the α-region (solid solution) and shortening of the isotherm plateaus accompanied with significant reduction of hysteresis. The Co-substituted compositions were found to be of particular importance among CeNi5-based systems because of their unique capability to reduce hysteresis without decreasing equilibrium pressures. This effect was due to nearly equal atomic radii of Ni and Co, and therefore, unaffected lattice parameters, and on the other hand, to the appearance of an intermediate hydride phase.