Atomic structure and enhanced thermostability of a new structure MgYZn4 formed by ordered substitution of Y for Mg in MgZn2 in a Mg-Zn-Y alloy

A new phase MgYZn₄ in Mg-Zn-Y alloy was studied using aberration-corrected scanning-transmission electron microscopy and first-principles calculations. Nanometer-sized MgYZn₄ precipitates were formed through ordered substitutions of Y with 50% Mg atoms in MgZn₂. MgYZn₄ has an orthorhombic structure with a space group of Pmnn, and lattice parameters a =5.2965 Å, b =9.4886 Å, and c =8.5966 Å. Importantly, both size and structure of MgYZn₄ are stable at 625 K for 5 h, showing higher thermostability than MgZn₂, which should be important for applications at elevated temperatures. The enhanced thermostability of MgYZn₄ is attributed to the lower formation energy and bonding enhancement due to Y substitution.