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

Abstract

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 = 0·82nm, b = 2·06 nm and c = 2·35nm, and the space group Pmn2₁ (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 Al₇₀Co₂₀Pd₅ alloys. The structural relationships between the W-phase and decagonal quasicrystal are discussed.