Quasicrystals and their crystalline homologues in the Al-Mn-Cu ternary alloys

Abstract

Electron diffraction and high-resolution electron microscopy have been employed to differentiate among icosahedral, decagonal and crystalline particles that occur in as-cast and rapidly solidified Al-Mn-Cu alloys. The resemblance between decagonal quasicrystals and crystals in their electron diffraction patterns is striking. The crystalline structure is based on the orthorhombic 'Al₃Mn' structure, but also a new monoclinic phase called 'X' has been discovered and described here. The present observations are also closely related to the orthorhombic structures in Al₆₀Mn₁₁Ni₄. The occurrence of fine-scale twinning and fragmentation into domains explains the complex diffraction effects.