Long dislocations of 1-2 mm length in an A162Cu253Fel2.1 icosahedral quasi-crystal (IQC) were investigated by means of white-beam synchrotron radiation x-ray topography for the fim time. The direction of the Burgers vector of a dislocation was determined by the invisibility conditionto beparallel to thesix-dimensional vector i[O, -1. 1. -1.0, I]. thephysiwlsubspace component of which is pxallel to a two-fold axis of the IQC. This result is consistent with that determined by a trssmission eleHrOn microscopy sNdy.

AbsImcL lo this paper. [he I20 keV Ar'-ion.in~di~tion-rnduced phzc uansformxtion from the A I ~z C U Z I . I F ~I ~J icosahedra quvicryswl (m) io B2(CsCI)-bd phses has been shldied by mcms of transmission clcCVOn microscopy. Ihc dose dependence of the Aii ion irndiation effeci and the subsequent w n r u hexing and cooling bckniourr after irndwlion have becn in,esoga[ed. The ekpenmencrl m u l l s show ha1 rhe Ar'-imdiaiioncnhced diffusion m amlenle the vulslormation from the A l o ? C u ~~F c . ~~ IQC to a B 2 -r ) ~ or BZ-bmd p h m Y mom IemperaiLre and that !his 62 oc B2-b~sed phase m u f o r m IcvwJel) to ihe iw whcn dx Ar+ dose is equal to or lower than IO" Ar+ cm-z and the temperature is increased to about lMl0 K.

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