Long-period stacking ordered structure in Mg-Y-Co-Ni alloy

Amorphous samples of Mg 84 Y 9 Co 2 Ni 3 (at%) were prepared and subjected to in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) measurements during annealing, followed by extended X-ray absorption fine structure (EXAFS) experiments. The SAXS and WAXD profiles indicated the formation of the 18R-type long-period stacking ordered (LPSO) structure after heat treatment at 673 K. EXAFS spectra suggested the presence of both Co and Ni atoms within the L1 2 -type solute clusters. Ab initio calculations for the quaternary LPSO phase were performed, and the results indicated that the mixing of Co and Ni in a single L1 2 -type cluster stabilizes the 18R-type LPSO phase. Furthermore, the relaxed cluster structure exhibited dimensions consistent with those observed in the EXAFS measurements. • Mg-Y-Co-Ni quaternary alloy was investigated. • SAXS and XRD revealed LPSO formation without other compounds. • EXAFS demonstrated both Co and Ni inclusion in L12-type cluster. • Ab initio calculation confirmed stability of the quaternary LPSO structure.