1 Ames Laboratory
2 Department of Physics and Astronomy,
3 Department of Material Science and Engineering,
4 Deptartment of Geological and Atmospheric Sciences,
Iowa State University, Ames, Iowa 50011.
High-quality, single-grain samples of decagonal Al-Ni-Co quasicrystals with volumes of up to 0.8 cm3 and an approximate composition of Al72Ni11Co17 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 and diffuse scattering in the odd n layers, indicative of a structure intermediate between 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 nonmetallic, with a broad maximum around 180 K, and a value of approximately 310 µOhm-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 perpendicular to c.
|Accepted; Philos. Mag. B (1999).|