Short-range and medium-range order in liquid and amorphous Al 90Fe 5Ce 5 alloys

Abstract

The liquid and amorphous structures of an Al 90Fe 5Ce 5 alloy have been studied by X-ray diffraction. Distinct prepeaks (the prepeak occurs at values of scattering vector Q=1–2 Å −1 and in front of the main peak) have been found in the structure factors of the liquid and amorphous alloys. The structural correlation length (or the cluster size) of the chemical short-range order corresponding to the prepeak in the liquid alloy increases with decreasing temperature. After glass formation, the structural correlation length is much larger and the amount of structure corresponding to the prepeak increases with decreasing quenching temperature, but the structural unit size remains constant. The position of the prepeak shifts to smaller Q-values as the concentration of Ce increases. The addition of Ce can improve the interaction between atoms, so it is favorable to Al-based glass formability. The structural unit corresponding to the prepeak is an icosahedral quasi-crystalline structure with Fe as the central atom; this stable medium-range order has already formed in the liquid alloy and can be preserved in the amorphous alloy.