FE-57 MOSSBAUER AND POSITRON LIFETIME STUDIES OF AL-CU-FE QUASI-CRYSTALS

Al61.4Cu22.7Fe15.9, Al63.2Cu21.8Fe15 and Al71Cu14Fe15 have been studie d by Mossbauer, positron annihilation and X-ray diffraction techniques . The positron lifetime, measured as a function of temperature, in Al6 1.4Cu22.7Fe15.9 shows a two-step increase. This is found to be due to the dynamics of phasons associated with Al and Cu, having activation e nergies of 0.43 eV and 0.78 eV respectively. In the case of Al71Cu14Fe 15, a phase transformation from the quasicrystalline-crystalline phase at approximate to 550 degrees C is observed.