  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.
