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 out for an icosahedral quasicrystalline Al-Cu Ru alloy under high pressure in quasihydrostatic conditions. The EXAFS measurements, performed above the Cu 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 diffraction. Diffraction measurements of the bulk modulus B-0 and its pressure 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 distance decrease monotonically with increasing pressure, showing the stability of the icosahedral phase, the widths of the Brags peaks show a systematic step broadening at about 10 GPa before following a plateau behaviour at higher pressures. At the same time, the sigma disorder parameter, associated with the first neighbour distance around Cu atoms, decreases with increasing pressure up to about 10 GPa, then remains almost constant. Both types of evolution could be the fingerprint of an order-disorder transformation, possibly induced by some phason disorder arising during the compression.