Predicted structures and temperature-dependent stability of Mg–Yb–Zn intermetallic compounds

To determine whether stable ternary intermetallic compounds exist in the Mg–Yb–Zn system, we used the USPEX evolutionary algorithm combined with first-principles calculations to perform a global structure search, and obtained five low-energy candidates: MgYbZn 2 , MgYb 2 Zn 2 , MgYbZn 3 , MgYbZn 4 , and MgYbZn 5 . Subsequently, the thermodynamic stability, mechanical stability, and dynamic stability of the phases were determined by calculating the 0 K convex hull, elastic constants, and phonon spectra, respectively. The quasiharmonic approximation was also employed to calculate the thermodynamic properties of the predicted structures at finite temperatures, allowing us to assess how temperature tunes the relative stability of these phases. The results show that MgYbZn 5 is a low-energy metastable phase at 0 K, but the contribution of lattice vibrations gradually increases with rising temperature, driving it into the finite-temperature convex hull region at approximately 590 K. MgYb 2 Zn 2 is located on the convex hull at low temperatures, but its stability gradually decreases with increasing temperature, and it progressively moves away from this region. All five ternary phases are metallic, and their bonding combines metallic interactions with weak covalent interactions, which is closely related to their mechanical stability and elastic behavior. The predicted orthorhombic structure of MgYbZn 5 received preliminary experimental support from high-resolution transmission electron microscopy and selected-area electron diffraction, in conjunction with QSTEM simulations. This work provides an understanding of the structural characteristics and thermodynamic stability of Mg–Yb–Zn ternary phases, offering a theoretical basis for exploring their potential roles as second-phase constituents in Mg alloys.