Oxides, Chalcogenides and Metallic Glasses

The number of studies in this field has been growing very rapidly in the past few years since there is a great demand from industry for improved classical glasses 

X-ray scattering studies often lead to ambiguous answers concerning the local structure, especially in the case of multicomponent glasses. As EXAFS provides a partial radial distribution function, this method becomes very powerful when the distribution relative to each atomic species can be joined up. This situation is often encountered in metallic glasses. 

Maeda et al. have prepared glassy samples of Feg Zr g alloy by the meltquenching technique. EXAFS data were collected on both edges at Tsukuba Photon Factory. Results of the curve fitting are given in Table 6. 

However, according to Raoux and Frank these underestimated coordination numbers and too short bond distances are caused by an intrinsic limitation of EXAFS, 

The EXAFS on Y-edge is very well fitted by a two shell model 3.3 Cu at 2.83 A and 1.5 Cu at 3.03 A. But, in this second shell, the coordination number is extremely ambiguous as it can be raised to 6 by changing the Debye-Waller factor from 0.1 A to 0.15 A. The study of the X-ray scattering data allows to solve this problem. The fitting of the radial distribution functions gives evidence of Cu—Cu interactions. And, finally, the only model which leads to a good reconstruction of the X-ray RDF and of the EXAFS spectrum implies four different subshells, two of them for Cu—Cu correlations and the other ones for Cu—Y correlations. Interatomic distances and coordination numbers appear in Table 7. 

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