Polytypism in a decagonal quasicrystalline Al-Co phase

A decagonal quasicrystalline phase has been produced in rapidly solidified binary Al-14 to 25 at.% Co and ternary Al-20 at.% Co-5 at.% Si alloys. Observation of periodicity along one of the directions in the electron diffraction patterns has confirmed the decagonal nature of the phase. Variations in periodicity ranging from 4 to 16 Å suggest that a polytypism-like phenomenon occurs in these phases. By in situ hot-stage electron microscopy, it can be shown that one polytype transforms into another. Reasons for the formation and transformation of polytypes in decagonal quasicrystalline phases are discussed.