Change in environmental structure around Al in Zr₆₀Ni ₂₅Al₁₅ metallic glass upon crystallization studied by nuclear magnetic resonance

In order to investigate the structural evolution around Al, pulse NMR experiments were carried out on ²⁷Al in the Zr₆₀Ni ₂₅Al₁₅ metallic glass and the related crystalline compound, Zr₆NiAl₂. Different chemical shift peaks were observed around 2750 and 3000 ppm in the as-quenched Zr₆₀Ni ₂₅Al₁₅ and crystalline compound, Zr₆NiAl ₂, respectively. Considering that the capped triangular prism of Zr₉Al₃ is formed around Al in the Zr₆NiAl ₂ crystal, chemical correlation pairs of Al-Zr and/or Al-Al are fairly faint while that of Al-Ni may be dominant instead in the as-quenched state. These results suggest an inhomogenous chemical bonding nature in the Zr₆₀Ni₂₅Al₁₅ metallic glass. The resonant peaks around 3000 ppm, which were distinctive in the Zr₆NiAl₂ crystal, appeared and became stronger upon crystallization through the relaxed state. Thus, drastic change in the local atomic configuration around Al was confirmed so as to form the unlike chemical correlation pairs of Al-Zr upon crystallization. The high glass-forming ability of the Zr₆₀Ni ₂₅Al₁₅ metallic glass should be attributed to the difficulties of significant atomic redistribution of the constituents around Al.