P. Donnadieu et C. Degand, EVIDENCE OF INTERMEDIATE STATES BETWEEN APPROXIMANT CRYSTAL AND QUASI-CRYSTAL, Philosophical magazine. B. Physics of condensed matter. Structural, electronic, optical and magnetic properties, 68(3), 1993, pp. 317-328
We report transmission electron microscopy investigations on the Al6Li
3Cu (quasicrystal)-Al5Li3Cu (crystal) interface. This interfacial area
is not sharp but displays intermediate states. A detailed analysis of
the diffraction patterns reveals that the transformation involves a p
lanar defect organization. The defect network, periodically organized
at low defect density, becomes aperiodic when the defect density incre
ases. This complex organization suggests that diffusion rates are very
low in quasicrystals. New conditions for annealing Al6Li3Cu quasicrys
tals are then determined that subsequently improve the quasicrystallin
e order. Fine lines of diffuse scattering in annealed samples still re
main as imperfections. We interpret these lines as a precursor state o
f a new rhombohedral approximant crystal. These observations provide a
sequence of intermediate states to discuss in relation to the deviati
on from icosahedral symmetry in diffraction patterns and diffusive/dis
placive transformations.