Structural study of approximant phases of Al-Cu-Fe quasicrystals under high pressure

X-ray-diffraction experiments under high-pressure conditions were performed on two high-order approximant phases of the icosahedral Al-Cu-Fe quasicrys tal. The rhombohedral and pentagonal samples were compressed under quasihyd rostatic conditions up to 35 GPa. We did not observe clear evidence for str uctural transformation in either sample. The most prominent feature observe d was a broadening of the Bragg peaks with increasing pressure. This behavi or has been compared with the one exhibited by the parent related structure (i-Al-Cu-Fe) and by a low-order cubic approximant structure (a-Al-Cu-Fe-Si ). The modifications in the diffraction patterns are preserved after pressu re release. The peak broadening has been related with the development of a particular phason-strain field. This kind of interaction is explained with the help of group-theoretical arguments proposed by Ishii. [S0163-1829(98)0 9037-7].