Fe-57 Mossbauer study of icosahedral Al55Si7Cu25.5Fe12.5 and its 1/1 approximant

The icosahedral Al55Si7Cu25.5Fe12.5 alloy and its 1/1 approximant of the sa me composition have been studied with Fe-57 Mossbauer spectroscopy (MS) in the temperature range 4.3-473.2 K. The average quadrupole splitting decreas es with temperature as T-3/2 for both alloys and its value is significantly larger for the icosahedral alloy. The vibrations of the Fe atoms in both a lloys are well described by a simple Debye model, with characteristic Mossb auer temperatures of 454(22) and 491(25) K for the icosahedral and approxim ant alloys. The local properties measured by zero-field Fe-57 Mossbauer spe ctroscopy are insensitive to the different nature of the long-range order, quasicrystalline vs. crystalline, in the investigated alloys. (C) 2000 Else vier Science B.V. All rights reserved.