HYDRIDING PROPERTIES OF THE ZR(CR0.5NI0.5)(ALPHA) -THAN-OR-EQUAL-TO-ALPHA-LESS-THAN-OR-EQUAL-TO-3.5) ALLOY SYSTEM

We studied a series of Zr(Cr0.5Ni0.5)(alpha) alloys (1.75 less than or equal to alpha less than or equal to 3.5) in order to investigate the effect of the stoichiometry and the influence of secondary phases on the electrochemical capacity. The main phase in the alloys is the hexa gonal C14 Laves phase for alpha less than or equal to 2 and the cubic C15 Laves phase for alpha>2. The secondary phases Zr2Ni7 and Zr2NiHx ( for alpha=1.75), as well as Zr7Ni10 and precipitated Cr (for alpha gre ater than or equal to 2) were found together with the Laves phases. Th e highest capacity was found for alpha=2 (383 mAh g(-1), H/M=1.0, disc harge current 4 mA g(-1)) and the amount of the secondary phase Zr7Ni1 0 is 11%. Normalization of the capacity with regard to the relative am ount of Laves phase in the alloy gives the highest value for alpha=2.2 5 where only 7.5% Zr7Ni10 was found. The absolute capacity measured at a low discharge current depends mainly on the cell volume of the Lava s phase whereas the kinetics are determined by the binary Zr-Ni phases . More important than the exact amount is the type of binary Zr-Ni pha se. (C) 1998 Elsevier Science S.A.