A new crystalline phase related to an Al–Ni–Co decagonal phase

Abstract

A new crystalline phase (called ‘W-(AlNiCo) phase’), which is closely related to Al–Ni–Co decagonal quasicrystals with 0.4 nm and 0.8 nm periodicity, has been found in an Al 72.5Ni 7.5Co 20 alloy annealed at 950°C. The W-(AlNiCo) phase has a monoclinic structure with lattice parameters a=3.99 nm, b=0.82 nm, c=2.36 nm and β=90°, and the space group of Cm (No. 8). Structural characteristics of the W-(AlNiCo) phase and the resemblance to those of an Al–Ni–Co pentagonal quasicrystal are discussed from atom-scale observations using high-angle annular detector dark-field scanning transmission electron microscopy and high-resolution electron transmission microscopy.