The decagonal quasicrystal formed from an Al–Pd–Mn icosahedral quasicrystal

We present a detailed investigation on the decagonal quasicrystal (D-phase) formed from an Al-Pd-Mn icosahedral quasicrystal (I-phase) through a solid-state phase transformation, including its formation, compositional and crystallographical relationships with the matrix I-phase, growth mode, and structural characteristics. The as-melt-spun Al₇₀Pd₂₀Mn₁₀ alloy contains only I-phase. By annealing at 800 °C, the D-phase is found to grow cpitaxially from the I-phase to establish a D/I two-phase equilibrium with distinctly different composition between them. The D-phase exhibits a stepped growth interface, which consists of a facet plane, formed by sharing the tenfold plane with a fivefold plane of the matrix I-phase, and some ledges across it. The growth of the D-phase into the I-phase proceeds through lateral movement of the ledges along the tenfold plane. High-resolution electron microscopy reveals that the structure of the D-phase is constructed by an aperiodic arrangement of decagonal atom clusters with definite linkages and long-range quasiperiodic correlation.