Synthesis of Ti-Zr-Ni amorphous and quasicrystal powders by mechanical alloying, and their electrochemical properties

Mechanical alloying of Ti₄₅Zr_38–xNi_17+x and Ti_45–xZr₃₈Ni_17+x (0 ≤ x ≤ 8) elemental powders produced an amorphous phase, but subsequent annealing converted the amorphous phase into an icosahedral quasicrystal phase, along with a Ti₂Ni-type phase. The discharge capacities, measured in a three-electrode cell at room temperature for both the amorphous and quasicrystal electrodes, increased with increasing Ni substitution for Zr or Ti. The highest discharge capacities, which were about 60 mAh/g for the amorphous electrode and 100 mAh/g for the quasicrystal electrode, were obtained from (Ti₄₅Zr₃₀Ni₂₅) after substitution of Ni for Zr. For the Ti₄₅Zr₃₀Ni₂₅ composition, the discharge performance of the quasicrystal electrode was stable over charge/discharge cycling, but that of the amorphous electrode gradually decreased with cycling. The structure of the quasicrystal phase in the electrodes was stable, even after 15 charge/discharge cycles, but the amorphous phase converted to a (Ti, Zr)H₂ f.c.c. hydride.