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

摘要

The structural, elastic, and electronic properties of newly synthesizedZr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminateshave been studied using first-principles density functional theory (DFT)calculations for the first time. Theoretical Vickers hardness has also beenestimated for these compounds. All the calculated results are compared withexperimental data and also with that of recently discovered Zr2AlC phase, whereavailable. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sncontaining MAX compounds. The calculated structural parameters are found to bein good agreement with the experimental data. The single crystal elasticconstants Cij and other polycrystalline elastic coefficients have beencalculated and the mechanical stabilities of these compounds have beentheoretically confirmed. The bulk modulus increases and the shear modulusdecreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculatedelastic moduli show that these Bi/Sn/Sb containing MAX phases are moreanisotropic than Zr2AlC, and have a tendency towards ductility. The Vickershardness decreases in the Bi/Sn/Sb containing compounds. Further, theelectronic band structures and electronic density of states (EDOS) arecalculated and the effects of different elemental substitution on theseproperties are investigated. The electronic band structures show metalliccharacteristics with contribution predominantly coming from the Zr 4d orbitals.Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level tosome extent. Possible implications of the theoretical results for theserecently discovered MAX nanolaminates have been discussed in detail in thispaper.