Formation and structures of decagonal quasi-crystals in the Al–Ni–Ru system

Two new decagonal quasi-crystals (D-phases), which have periods of 0.4 and 1.6 nm, respectively, have been found to form with different compositions in conventionally solidified Al–Ni–Ru alloys. The diffraction patterns of these two D-phases display a large number of sharp diffraction spots located at exact tenfold symmetry positions and almost no diffuse streaks, indicating that they are highly ordered quasi-crystals. The D-phase with 0.4-nm periodicity exhibits a pronounced S1-type superlattice order. The D-phase with 1.6-nm periodicity can be formed as a major phase by annealing at around 900°C. By means of high-resolution electron microscopy, the structural characteristics of the D-phase with 1.6-nm periodicity have been revealed.