PRESSURE-INDUCED PHASE-TRANSITION IN ICOSAHEDRAL AL-LI-CU QUASI-CRYSTALS

We report in-situ extended X-ray absorption fine-structure (EXAFS) stu dies of icosahedral Al6Li3Cu quasicrystals, without any aluminium exce ss, under a high pressure in quasihydrostatic conditions. The EXAFS ex periments have been performed at the Cu K absorption edge from ambient pressure up to 33 GPa and give the variation in the average distance of first neighbours around copper atoms against pressure. This average distance decreases monotonically with increasing pressure up to 12 GP a, remains almost constant up to 20 GPa and then increases. This incre ase in the interatomic distance is interpreted as the fingerprint of a phase transition. The relative first-neighbour distance has been fitt ed, up to 12 GPa, by a Murnaghan equation of state so that the zero-pr essure bulk modulus is B-0 = 71 GPa for a first derivative B-0' = 6. T his Bo local value found around copper atoms is close to the overall b ulk modulus of pure aluminium. After release of the pressure, the Al6L i3Cu quasicrystal shows spectacular 'metastable' properties.