Atomic-scale mapping of twins and relevant defective structures in Al₂₀Cu₂Mn₃ decagonal approximant

Abstract

Twins or multiple twins occur frequently in the orthorhombic Al₂₀Cu₂Mn₃ approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al₂₀Cu₂Mn₃ approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al₂₀Cu₂Mn₃ approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Keywords:

• Transmission electron microscopy
• decagonal approximant
• twins
• defects