High-order crystal approximant structures in TiZrNi alloys

We report the discovery of two high-order crystal approximants in rapidly quenched Ti₅₄Zr₂₆Ni₂₀ alloys. The diffraction patterns at first appear to belong to the icosahedral phase, but detailed transmission electron microscopy (TEM) studies reveal distortions that lower the symmetry. The diffraction patterns from one phase can be indexed to a 3/2 cubic rational approximant structure; those from the second phase can be indexed to a 5/3 cubic rational approximant. This is the first report such high-order approximants in any Ti-based alloy. Unlike all known Ti-based quasicrystals, no localized diffuse scattering is observed in the diffraction patterns from these approximants.