EXAFS and Mössbauer studies on local atomic structure in an amorphous Fe–B–Si alloy

Local atomic structures of an amorphous Fe79B16Si5 alloy and the structural changes by thermal annealing (structural relaxation) have been studied by extended X-ray absorption fine structure (EXAFS) and Mössbauer measurements. The structural analyses indicate that the interatomic distance of Fe–Si is larger than that of Fe–B and is close to the Fe–Fe distance. Such geometry becomes more obvious after structural relaxation. Discussions based on the structural model composed of capped trigonal prisms suggest that Si atoms do not locate at the central site of trigonal prisms, but substitutionally occupy the sites of Fe atoms at the vertices. During structural relaxation, the distance of Fe–B decreases and that of Fe–Fe is slightly shortened, while the Fe–Si distance remains unchanged. The coordination number of B atoms around Fe decreases but that of Fe atoms increases. The coordination number of Si around Fe is almost constant. The increase in coordination number of Fe around Fe during the structural relaxation is also confirmed by the Mössbauer effect study.