HIGH-PRESSURE X-RAY-DIFFRACTION OF ICOSAHEDRAL AL-CU-RU AND AL-PD-RE QUASI-CRYSTALS

We report in-situ X-ray diffraction results in icosahedral Al-Cu-Ru an d Al-Pd-Re quasicrystals under a high pressure in quasihydrostatic con ditions, at room temperature. Both types of quasicrystal remain icosah edral over the pressure range from ambient pressure up to 35 GPa, ther eby showing a remarkable stability under pressure. The relative volume change V//V-0 has been fitted to a Murnaghan-type equation of state s o that the zero-pressure bulk modulus is B-0 = 128 GPa in Al-Cu-Ru and 180 GPa in Al-Pd-Re for a first derivative B-0' = 5. While V/V-0 rati o decreases monotonically with increasing pressure, the widths of the Bragg peaks show a stepped broadening at 10 GPa for Al-Cu-Ru and at 7. 5 GPa for Al-Pd-Re before following a plateau behaviour at higher pres sures. This is interpreted by some phason disorder which stabilizes th e icosahedral symmetry.