Structural Change of Amorphous Mg₇₀Zn₃₀ Alloy under Isothermal Annealing

Abstract

Atomic structure of amorphous Mg–Zn alloys of near eutectic composition and the structural change toward the crystalline Mg₅₁Zn₂₀ under isothermal annealing at 350 K are investigated by X-ray diffraction and EXAFS. The structure factors and the reduced radial distribution functions obtained from the X-ray diffraction and the near neighbor partial radial distributions of Zn–Zn and Zn–Mg pairs from the EXAFS show that i) the amorphous state is random aggregate of chemical and structural units which have more or less regular polyhedral configurations and topologically similar to those in the crystalline Mg₅₁Zn₂₀, ii) in the first stage of annealing these units change their shape and size to enhance coherency in spatial relation with neighboring units, iii) in the second stage the units are further deformed to establish the long range order of the crystalline Mg₅₁Zn₂₀.