The study of Al3(Mn, Pd) crystal and Al–Mn–Pd decagonal quasicrystal by spherical aberration-corrected scanning transmission microscopy and atomic-resolution energy dispersive X-ray spectroscopy

Abstract

An Al3Mn-type Al3(Mn, Pd) crystal and an Al–Mn–Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al–Mn–Pd DQC have been interpreted. Pd and Mn atomic positions in the Al–Mn–Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2 nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al–Mn–Pd DQC structure.