The crystal structure of a new crystalline phase in the al-pd-cr alloy system, studied by high-resolution electron microscopy

The structure of a new crystalline phase (O-phase) in an Al₇₂Pd₁₈Cr₁₀alloy, which is closely related to an AI3M11 crystalline phase and the Al-Pd-Mn decagonal quasicrystal, was investigated by electron diffraction and high-resolution electron microscopy. The O-phase has an orthorhombic structure with the lattice parameters a = 1-25 nm, b = 3-28 nm and c = 2-38 nm, and the space group is Pmmn (no. 59). This structure is characterized as a periodic tiling constructed with two types of tiles, a squashed hexagon and a star-shaped pentagon, formed with pentagonal atom columns which are structural units in the Al3Mn crystalline phase and in Al-Pd-Mn decagonal quasicrystal. Structural relationships among the O-phase, the decagonal quasicrystal and some crystalline phases are discussed.