Structural relationship and mutual transformation of approximants of the decagonal Al-Co-Ni phase

Apart from the decagonal phase, several different approximant structures we re observed in the Al-Co-Ni alloy system. In this work, specimens with a co mposition of Al71Co14.5Ni14.5 are investigated by conventional acid high-re solution transmission electron microscopy. The structural relationships bet ween two approximant phases are studied in detail. Simplified atomic models of these structures are derived from high-resolution electron microscopy a nd verified by image contrast simulation. A transition between the two appr oximants is possible by changing only a few atomic positions. Nevertheless, these minor changes are sufficient to produce rather striking changes in h igh-resolution electron microscopy images. (C) 2000 Elsevier Science B.V. A ll rights reserved.