Microstructure and hydrogen-absorption properties of Zr-Ni-Mn ternary alloys

As a fundamental study of AB₂-type Laves phase alloys for use of the Ni/MH rechargeable battery, the relationship between the structure and the hydrogen-absorption properties was investigated for the annealed Zr(Ni_1-xMn_x)₂ and ZrNi_nMn_y (n=1.0, 1.1, 1.2, 1.3 and 1.4) alloys. For the Zr(Ni_1-xMn_x)₂ alloys, a secondary phase with a low Mn content existed along with a main C15-type Laves phase, whose volume fraction decreased with increasing Mn content. It was clarified that the hydrogen storage capacity increased with decreasing volume fraction of the secondary phase. On the other hand, the capacity of the alloys with the single C15-type Laves phase decreased with increasing Mn content. A clear relationship was found between the hydrogen-absorption properties and the lattice parameter of C15-type Laves phase, which decreased with increasing Mn content. The hydrogen storage capacity increased with increasing unit cell volume, while the desorption pressure of hydrogen decreased. It was suggested that ZrNi_1.3Mn_1.1 alloy was the potential alloys investigated for the rechargeable battery.