Czochralski growth and characterization of large decagonal Al–Co–Ni quasicrystals

In the ternary Al–Co–Ni system, decagonal quasicrystals occur that are thermodynamically stable and can be grown using rather conventional crystal growth techniques at near-equilibrium conditions. Detailed studies of the Al-rich part of the ternary phase diagram including the primary crystallization field of the decagonal phase are known from the literature. Using these data quasicrystal growth by the Czochralski method from off-stoichiometric (Al-rich) melts has proved to be successful. In a series of growth experiments with varying Co:Ni ratio along the 1050 and 1100°C isotherms, single-grain quasicrystals up to 1 cm3 in size have been grown. Use was made of very low growth rates (0.2–0.5 mm/h) as to meet the needs of the constitutional supercooling criterion as well as those arising from the anisotropic growth kinetics of the decagonal phase. The segregation behaviour was studied by electron probe microanalysis (EPMA) measurements concerning the change in the Al concentration during growth and the shift in the Co:Ni ratio which marks the main extension of the decagonal stability region.