X-ray absorption and diffraction spectroscopy of icosahedral Al-Cu-Fe quasicrystals under high pressure

Abstract

We report in-situ extended X-ray absorption fine structure (EXAFS) and X-ray diffraction studies of quasicrystals under high pressure quasihydrostatic conditions. The EXAFS and diffraction experiments are combined for the first time to give a joint evolution of the short-range and long-range atomic order with pressure. EXAFS experiments performed at the Fe and Cu K absorption edges have been carried out for an icosahedral Al₆₂Cu_25.5Fe_12.5 alloy from ambient pressure up to about 8 GPa (Fe edge) or 35 GPa (Cu edge). The local order around Fe and Cu atoms has thus been obtained as a function of pressure. X-ray diffraction patterns have been obtained for the same quasicrystal up to 35 GPa and these have given a variation in the 6D lattice parameter with pressure. A remarkable result is that the quasicrystal remains icosahedral up to the highest pressure. The evolution of the 6D lattice parameter and of the first-neighbour distances has provided values of the zero-pressure bulk modulus and of its first derivative by fitting a Murnaghan equation of state to the data. These values are different for the Fe and Cu environments. Furthermore, the “local” value found for Cu atoms is, at ambient pressure, close to the “mean” value found by diffraction but differs markedly from this value at high pressure.