Local atomic structures in amorphous Fe70M10B20 (M = Cr, W, Nb, Zr and Hf) alloys with different ΔTx values were studied by the ordinary X-ray diffraction, anomalous X-ray scattering and EXAFS methods. Their local the atomic structures basically resemble each other, i.e. a random network structure of triangular prisms. Only difference in local atomic structure is a shape of the local structural unit. In the amorphous alloys containing M elements larger than Fe atoms, the prisms show distorted shapes due to a size difference Δr between M and Fe. A linear relation between Δr and ΔTx, and a comparison of their crystallization processes suggest us that their thermal stability is attributed to difficulty in rearranging the irregular structural units because of a non-zero Δr value.
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