The Clustering of Zn6Y9 and its Predominant Role in Long Period Stacking Order Phases in Mg-Zn-Y Alloys: A First-Principles Study

The local structures of Zn and Y in the long period stacking order (LPSO) phase in Mg-Zn-Y system were investigated by first principles calculations in details. The clustering of Zn and Y atoms ranging from single stacking fault layer to four consecutive layers was explicitly demonstrated. The calculations indicate that Zn and Y atoms prefer clustering in the form of Zn6Y9 embedding in ABCA-type building block to the random or ordered arrangements of Zn and Y atoms being enriched in two stacking fault layers. The cluster of Zn6Y9 can be regarded as the ideal stoichiometric component of LPSO and it plays a predominant role in the LPSO phases. The formation of LPSO phases is highly associated with the Zn6Y9 cluster and its derivatives.