ELEMENTARY DIFFUSION JUMP OF IRON ATOMS IN INTERMETALLIC PHASES STUDIED BY MOSSBAUER-SPECTROSCOPY .2. FROM ORDER TO DISORDER

We determine the elementary diffusion jump mechanism of Fe atoms in B2 ordered Fe-Al single crystals (Fe contents 50.5, 55 and 66 at.%) by m eans of quasielastic Mossbauer spectroscopy at Fe-57. The mechanism ob viously follows the same logics irrespective of the alloy composition: it is a jump into an antistructure site on the Al sublattice, followe d by a jump back to a regular site on the Fe sublattice. Close to stoi chiometry Fe50Al50 the Fe atom resides on the antistructure site only for a small fraction of the time, but with increasing Fe concentration and at sufficiently high temperatures this fraction increases until t he residence time on the Al sublattice approaches the residence time o n the Fe sublattice. In Fe66Al37 there is no discontinuity in the Moss bauer spectra at the B2 --> A2 phase transition. This proves that shor t-range order decreases continuously in the region of the phase transi tion.