Structural stability, electronic, mechanical, and thermodynamic properties of the new MAX phases Mn2SiC1, Mn3SiC2 and Mn4SiC3: ab-initio calculations

In this work, we have studied the structural, electronic, elastic, and thermodynamic properties of the new Max phase's class Mn2SiC1, Mn3SiC2 and Mn4SiC3 (Mnn+1SiCn with n = 1, 2 and 3), using the linearly augmented plane wave method (FP-LAPW) based on density functional theory. The exchange-correlation potential is treated with the local density approximation LSDA. The formation energies calculated for all compounds showed that these compounds are thermodynamically stable. We found that the ferromagnetic (FM) configuration is more stable than the non-magnetic (NM) one, at their lattice parameters for all three compounds. Cohesive energy confirms the structural stability of all structures. The total magnetic moment increases with an increasing value of n. The band structure indicates that the three materials are electrically conductive. For the density of state, we see that there is no gap for these three materials; they exhibit a metallic nature which results from the fact that the Mn-3d states are dominant at the Fermi level. The peak of hybridization of the Mn-3d, and C-2p states leads to a strong covalent bond than that between the Mn-3d and Si-3p states in the low energy domain. 3p electrons in silicon elements can effectively alter the covalence and iconicity of bonds that govern compressibility, ductility, and even superconducting properties. The chemical bond in three compounds is a combination of covalent, ionic, and metallic nature. The main factors governing the electronic properties are the hybrid states Mn-3d, Si-3p, and C-2p, and the bond (p-d) stabilizes the structure. The elastic constants are calculated and the conditions of the criterion of mechanical stability are checked. In addition, we have calculated the bulk, and shear modulus, Young's modulus, Poisson's ratio, and anisotropy index. The quasi-harmonic Debye model was used to study the temperature-dependent thermodynamic properties of the Mnn+1SiCn (n = 1, 2, 3) compounds.