Stability of icosahedral Al-Cu-Fe and two approximant phases under high pressure up to 35 GPa

Abstract

A high-pressure X-ray diffraction study has been performed on a perfect icosahedral Al₆₂Cu_25·5Fe_12·5 (i-(Al—Cu—Fe)) phase at room temperature up to 33·5 GPa using a diamond-anvil cell to determine the equation of state. X-ray diffraction was undertaken in energy-dispersive mode on a synchrotron beam line.

The remarkable result is that i-(Al—Cu—Fe) remains icosahedral over this pressure range. The relative volume change V/V _o as a function of pressure is least squares fitted to a Murnaghan-type equation of state so that the zero-pressure bulk modulus B ₀ is 155 ± 10GPa, maintaining its pressure derivative B ^r ₀ = 2.

Two approximant phases with very similar chemical compositions but with different structures, a rhombohedral phase (Al_62·B Cu₂₆Fe_11·2) and a pentagonal phase (Al₆₄ Cu₂₄Fe₁₂), have been studied under the same conditions. No drastic modification of the diffraction spectra appears up to 33 GPa and both phases remain unchanged after release of the pressure. The relative volume change V/V ₀ is fitted to a Murnaghan-type equation of state with the same value of B ₀ for both approximants: B ₀ = 175 ± 16GPa, maintaining its pressure derivative B ^r ₀ = 2.