IRREVERSIBLE STRUCTURAL RELAXATION IN FE-B-SI AMORPHOUS-ALLOYS

Structural relaxation in Fe78B7Si15 and Fe75B10Si15 amorphous alloys w ith annealing has been studied by means of the measurements of electri cal resistance and Mossbauer spectroscopy. The electrical resistance o f as-prepared alloys decreased abruptly in the initial stages of annea ling and then attained a quasi-equilibrium value that depends on annea ling temperature. A model, combining the Ziman theory for resistance a nd free-volume model for viscous flow, was used to analyze the irrever sible decrease of resistance. The observed resistance changes were wel l reproduced with the model. The activation energy for annihilation of free volume was evaluated to be 154 kJ mol(-1) for the Fe78B7Si15 all oy and 222 kJ mol(-1) for the Fe75B10Si15 alloy from resistance change s. On the other hand, we observed a significant difference in the anne aling behavior of the average isomer shift and hyperfine field with ti me between these two alloys. This indicates that the local structural change during relaxation process differs much in both amorphous alloys . The observed difference in relaxation behavior between the two alloy s can be explained in terms of Dubois and Le Caer's structural model o f Fe-B-Si amorphous alloys. (C) 1997 Elsevier Science S.A.