In situ high pressure X-ray diffraction and EXAFS spectroscopy of icosahedral Al-Cu-Ru quasicrystals

In situ X-ray diffraction and EXAFS experiments have been carried earned ou t for an icosahedral quasicrystalline Al-Cu Ru alloy under high pressure in quasihydrostatic conditions. The EXAFS measurements, performed above the C u K absorption edge, have given the evolution of the local order around Cu atoms, which has been compared to that of the long range order yielded by d iffraction. Diffraction measurements of the bulk modulus B-0 and its pressu re derivative B-0' compare well with the 'local' values obtained around Cu atoms from the evolution of the mean first neighbour distance with pressure . While the six-dimensional lattice parameter and the first neighbour dista nce decrease monotonically with increasing pressure, showing the stability of the icosahedral phase, the widths of the Brags peaks show a systematic s tep broadening at about 10 GPa before following a plateau behaviour at high er pressures. At the same time, the sigma disorder parameter, associated wi th the first neighbour distance around Cu atoms, decreases with increasing pressure up to about 10 GPa, then remains almost constant. Both types of ev olution could be the fingerprint of an order-disorder transformation, possi bly induced by some phason disorder arising during the compression.