Hydrogenation properties and structural change of HfxZr7−xNi10 ()

Hf7Ni10 has the same crystal structure as Zr7Ni10, which shows several unusual hydrogenation properties such as reversible hydrogenation by irreversible phase transformation and structural change caused by hydrogenation followed by dehydrogenation, and its hydrogenation properties have been unknown. The phase relation and hydrogenation properties of HfxZr7-xNi10 alloys were investigated in the compositional range from Zr7Ni10 (x = 0) to Hf7Ni10 (x = 7). All the samples were obtained by arc melting followed by heat treatment in vacuum. The constituent phase was identified by the combination of X-ray diffraction and microscopic analysis and hydrogenation properties were examined by differential scanning calorimetry and Sieverts' method. No structural change from orthorhombic Cmca type to another one such as tetragonal I4/mmm type and orthorhombic Pbca type was observed for the addition of Hf and Hf was substituted for Zr in Zr7Ni10 in all the compositional range we examined. The lattice constant of the aimed phase decreased with an increase in Hf content. The measurements using differential scanning calorimetry indicated that the Hf-substituted alloys showed the same phase transformation as Zr7Ni10 in hydrogenation, that is the unusual phase transformation that an intermediate hydride phase appears only in dehydrogenation but not in hydrogenation. The transformation temperature decreased with an increase in Hf content.