Atomic structure of Al88Y7Fe5 metallic glass -: art. no. 113507

The structure of Al88Y7Fe5 metallic glass has been investigated by differential scanning calorimetry, x-ray powder diffraction, and x-ray absorption fine structure (XAFS) techniques. The amorphous alloy crystallizes according to the following scheme: amorphous ->alpha-Al+ residual amorphous ->alpha-Al+Al3Y+AlFeY. The atomic structure of the amorphous alloy was modeled by reverse Monte Carlo methods. The resulting structure indicates that the prepeak (at 1.42 A(-1)) in the static structure factor S(Q) is caused by contributions of distinct Y-Y, Y-Fe pairs. From the analysis of our XAFS spectra at the Fe and Y K edge the following characteristics of the local structure are found: The interatomic distance between Fe and coordinated Al atoms in the amorphous state is significantly (8.9%) shorter than the sum of the nominal metallic-state radii. The average coordination number is anomalously 36% reduced compared to the value derived from the dense-random-packing (DRP) model, using again the nominal metallic-state radii. On the other hand, the Y-Al distance as well as the number of Al atoms coordinating Y is close to the values predicted by the DRP model. These anomalous changes around the Fe atoms indicate a strong interaction between Fe and Al, which corroborate a covalent bonding. In connection with the values obtained from the XAFS data analysis, the effective atomic radii in the amorphous phase have been calculated. Consequently, applying them to the calculation of the atomic size factor (lambda=0.1076) confirms that Al88Y7Fe5 follows the rule of atomic size ratio for glass formation. (C) 2005 American Institute of Physics.