Czochralski growth and X-ray topographic characterization of decagonal AlCoNi quasicrystals

Abstract

Large single crystals of the decagonal AlCoNi phase were reproducibly grown by the Czochralski method from Al-rich melts. By using native seeds, it was possible to grow crystals with well-defined orientations, e.g. along the 10-fold periodic axis or parallel to one of the 2-fold axes. Quasicrystals, that had been pulled in periodic or quasiperiodic directions, were characterized by X-ray transmission topography at the synchrotron source (ESRF) and at laboratory sources using the Lang technique. Because of the metallurgical homogeneity of the grown quasicrystals, lattice parameter differences did not contribute to the topographic contrast, instead, orientation contrast dominated. A column-like substructure along the periodic direction could be revealed. From this it is concluded that crystal growth along a two-fold direction might be favourable with respect to minimizing defect spreading.

Acknowledgments

The authors would like to thank R. Wunderlich for surface preparation and P. Dreier for EPMA measurements. Financial support by the Deutsche Forschungsgemeinschaft under contract Gi 211/6 is gratefully acknowledged.