THE EFFECT OF TEMPERATURE ON STABILITY OF THE AL-CU-CO DECAGONAL PHASE

Melt-spun Al65Cu15Co20 ribbons annealed at 550-degrees-C for 62 days have been studied in high-resolution electron microscopy (HREM). No structural transformation of the decagonal phase has been observed. Using the centres of tenfold ring cluster, both HREM pictures for the long-term annealed and unannealed samples can be covered completely with Penrose tiles from set P1 and set P3, with the tile length 12-4 angstrom, which is a tau--1 scaling of our previous tile length (20 angstrom). Phason fluctuations calculated for both samples are found to be similar. The observed structures can be described by a random tiling model based on Penrose tiles from set P1 and P3, which is different from conventional random binary tiling. The important roles of composition and frozen-in phason disorder in the stability of the decagonal phase are discussed.