Crystallization of metastable phases in the Pd83Si17 amorphous alloy

The crystallization of the Pd83Si17 amorphous alloy started by formation of small crystallites. By comparisons of selected area electron diffraction patterns from the crystallites and patterns calculated from generated models we found that the first observed structures coincide with long range vacancy ordered structures derived from CsCl-type structure, known as τ-structures. The Pd atoms are in the corners and the Si atoms or vacancies are in the centers of basic cubic cell, respectively. It is possible to interpret the formation of these transition structures as consequence of occurrence of small areas with different chemical composition present in original amorphous structure as a result of rapid quenching. After ageing the τ-structures transform by diffusion to the stable Pd9Si2 structure.