Newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX phases: A first-principles study

The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results are compared with experimental data and also with that of recently discovered Zr2AlC phase, where available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn containing MAX compounds. The calculated structural parameters are found to be in good agreement with the experimental data. The single crystal elastic constants Cij and other polycrystalline elastic coefficients have been calculated and the mechanical stabilities of these compounds have been theoretically confirmed. The bulk modulus increases and the shear modulus decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated elastic moduli show that these Bi/Sn/Sb containing MAX phases are more anisotropic than Zr2AlC, and have a tendency towards ductility. The Vickers hardness decreases in the Bi/Sn/Sb containing compounds. Further, the electronic band structures and electronic density of states (EDOS) are calculated and the effects of different elemental substitution on these properties are investigated. The electronic band structures show metallic characteristics with contribution predominantly coming from the Zr 4d orbitals. Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to some extent. Possible implications of the theoretical results for these recently discovered MAX nanolaminates have been discussed in detail in this paper.