HAADF-STEM study of B-Mg-Ru approximant crystals.

Two-dimensional structures of decagonal approximant crystals have been studied in a B-Mg-Ru system where decagonal quasicrystals have been predicted. High-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) imaging confirms that four approximant phases, which form at high temperatures, can be described as tessellations of hexagon and boat subunits with the same atomic decorations as B11Mg5Ru13. The images also support the existence of bow-tie flip structures in the all four approximant crystals. Long periodicities in one direction up to 8.5 nm are interpreted to be caused by modulation of rows of boat tiles. [ABSTRACT FROM AUTHOR]