A new crystalline phase related to decagonal quasicrystals with non-central symmetry in Al-Co-Pd alloys

摘要

A new crystalline phase, related to decagonal quasicrystals with non-central symmetry, is found in conventionally solidified Al70Co20Pd10 and Al73Co22Pd5 alloys. The new crystalline phase, which is called a W-phase hereafter, has an orthorhombic structure with lattice parameters a = 0.82 nm, b = 2.06 nm and c = 2.35 nm, and the space group Pmn2(1) (No. 31). From electron diffraction and high-resolution electron microscopy observations of the W-phase, we propose a tentative structural model, which is constructed by modifying the structure of an Al-Ni-Co decagonal quasicrystal. A non-central symmetric decagonal quasicrystal with 0.4 nm periodicity is found in rapidly solidified Al70Co20Pd10 and A1(73)Co(22)Pd(5) alloys. The structural relationships between the W-phase and decagonal quasicrystal are discussed.