最近合成的（Zr1-xTix）2AlC（0 - x - 1）固溶体：M混合对物理性质影响的理论研究
Recently synthesized (Zr1-xTix)2AlC (0 - x - 1) solid solutions: Theoretical study of the effects of M mixing on physical properties
摘要：
采用密度泛函理论（DFT）研究了M原子物种混合对新合成MAX相（Zr 1-xTix）2AlC固溶体物理性质的影响。晶格常数随Ti含量的增加而减小，与实验结果吻合较好。计算了弹性常数Cij和其它多晶弹性模量。弹性常数满足这些固溶体的机械稳定性条件。发现常数C11、C33和C44随着Ti含量的增加而增加，直到x = 0.67，此后这些常数略有下降。C12和C13的趋势相反。弹性模量也被发现增加到x = 0.67，超过这一点，这些模量略有下降。Pughs比和Poissons比都证实了（Zr 1-xTix）2AlC的脆性。不同的各向异性因子揭示了这些固溶体的各向异性特征。费米能级的电子态能量密度（EDOS）的非零值表明（Zr_（1-x）Ti_x）_2Al_C具有金属性质。从电子结构中已经表明了共价键、离子键和金属键的混合物，其中由于Zr-4d态和C-2 p态的杂化而具有占主导地位的共价键。弹性刚度和弹性参数随x的变化与部分DOS（PDOS）和电荷密度分布有关。计算的德拜温度和最小热导率被发现增加与Ti含量，而熔化温度是最高的x = 0.67。x = 0.67的固溶体与两个端元Zr 2AlC和Ti 2AlC相比显示出改善的机械和热性能。对（Zr_（1-x）Ti_x）_2AlC的电荷输运性质的研究揭示了其饱和电阻率的金属本质。（Zr_（1-x）Ti_x）_2AlC在400 K时获得最大功率因数。
英文摘要：
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.
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