Recently synthesized (Zr1-xTix)2AlC (0 - x - 1) solid solutions: Theoretical study of the effects of M mixing on physical properties

The effects of M atomic species mixing on the physical properties of newly synthesized MAX phase (Zr1-xTix)2AlC solid solutions have been studied by means of density functional theory (DFT) calculations. The lattice constants in good accord with the experimental results, are found to decrease with Ti content. The elastic constants, Cij, and the other polycrystalline elastic moduli have been calculated. The elastic constants satisfy the mechanical stability conditions of these solid solutions. The constants C11, C33 and C44 are found to increase with Ti contents up to x = 0.67, thereafter these decrease slightly. A reverse trend is followed by C12 and C13. The elastic moduli are also found to increase up to x = 0.67, beyond which these moduli go down slightly. Pughs ratio and Poissons ratio both confirm the brittleness of (Zr1-xTix)2AlC. Different anisotropy factors revealed the anisotropic character of these solid solutions. A non-vanishing value of the electronic energy density of states (EDOS) at the Fermi level suggests that (Zr1-xTix)2AlC are metallic in nature. A mixture of covalent, ionic and metallic bonding has been indicated from the electronic structure with dominant covalent bonding due to hybridization of Zr-4d states and C-2p states. The variation of elastic stiffness and elastic parameters with x is seen to be correlated with partial DOS (PDOS) and charge density distribution. The calculated Debye temperature and minimum thermal conductivity are found to increase with Ti contents, while melting temperature is the highest for x = 0.67. The solid solution with x = 0.67 shows improved mechanical and thermal properties compared to that of the two end members Zr2AlC and Ti2AlC. The study of charge transport properties of (Zr1-xTix)2AlC reveals the metallic nature with saturated resistivity. The maximum power factor is obtained at 400 K for (Zr1-xTix)2AlC.
Comment: 16 pages, 7 figures, submitted to Journal of Alloys and Compounds