Structural Change of Al-Cu-Co Decagonal Quasicrystal Studied by High-Resolution Electron Microscopy

Abstract

We found that the stable decagonal quasicrystal of Al-Cu-Co undergoes a structural change at low temperatures. The Al₆₅Cu₁₅Co₂₀ alloy quenched from 800°C shows diffraction patterns with sharp spots placed at nearly perfect decagonal symmetry positions, but by annealing at 550°C the diffraction patterns show a remarkable change in the appearance of diffuse scatterings. High-resolution electron microscopy shows the transformation, at low temperatures, into a partially crystalline structure of a monoclinic unit cell with a=b=2 nm, c=0.4 nm and γ=108°.