STRUCTURAL VARIATIONS AND TRANSFORMATION BEHAVIOR OF THE AL68CU11CO21 DECAGONAL PHASE

The Al68Cu11Co21 decagonal phase was studied after annealing at 1000 degrees C for 24-760 h by transmission and scanning electron microscopy. The strong superstructure odd-n reflections in the [1,-2, 1, 0, 0] electron diffractograms were stable under annealing up to about 40 h. As a possible origin of the increased intensities of the odd-n reflections the formation of vacancy-ordered structures is discussed. The structure was modified by prolonged annealing. In several annealed samples a dense net of extra reflections overlapping the quasiperiodic reflections was observed. This observation was explained as an indication of the formation of metastable states during cooling. Differently ordered decagonal structures exhibited different transformation kinetics during cooling from high temperatures.