On the growth of decagonal Al-Ni-Co quasicrystals from the ternary melt

Abstract

High-quality, single-Frain samples of decagonal Al-Ni-Co quasicrystals with volumes of up to 0.8 cm³ and an approximate composition of Al₇₂Ni₁₁ Co₁₇ have been grown from the ternary melt. The precise growth methods and conditions are discussed in detail. X-ray diffraction patterns of crushed single grains and of single-grain samples are exceptionally sharp indicating a high degree of structural order with no evidence of second phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even n layers but diffuse scattering in the odd n layers, indicative of a structure intermediate between the Al₇₃Co₂₇ and Al₆₉Ni₃₁ end members. The electrical resistivity measured directly from cut bars for currents flowing perpendicular to the crystalline direction (i.e. perpendicular to the c axis) is non-metallic, with a broad maximum around 180 K, and a value of approximately 310 μω cm at 300 K. The resistivity for currents flowing parallel to the c axis is metallic and is almost an order of magnitude smaller in value than for i ⊢ c.