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

Abstract

The effects of M atomic species mixing on the structural, elastic, electronic, thermodynamic and charge transport properties of newly synthesized MAX phase (Zr 1-x Ti x ) 2 AlC (0 ≤ x ≤ 1) solid solutions have been studied for the first time by means of density functional theory (DFT) based first principles calculations. The lattice constants in good accord with the experimental results, are found to decrease with Ti content. The elastic constants, C ij , and the other polycrystalline elastic moduli have been calculated. The elastic constants satisfy the mechanical stability conditions of these solid solutions. The constants C 11 , C 33 and C 44 are found to increase with Ti contents up to x = 0.67, thereafter these decrease slightly. A reverse trend is followed by C 12 and C 13 . The elastic moduli are also found to increase up to x = 0.67, beyond which these moduli go down slightly. Pugh"s ratio and Poisson"s ratio both confirm the brittleness of (Zr 1-x Ti x ) 2 AlC. 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 (Zr 1-x Ti x ) 2 AlC 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 Zr 2 AlC and Ti 2 AlC. The study of charge transport properties of (Zr 1-x Ti x ) 2 AlC reveals the metallic nature with saturated resistivity. The maximum power factor (S 2 /=11.1×10 10 Wm -1 K -2 s -1 ) is obtained at 400 K for (Zr 1-x Ti x ) 2 AlC.

Recently synthesized (Ti1−xMox)2AlC (0 ≤ x ≤ 0.20) solid solutions: deciphering the structural, electronic, mechanical and thermodynamic properties via ab initio simulations

“…45,60 Moreover, we have investigated the effect of M mixing on the physical properties of (Zr,Ti) 2 AlC in our previous study. 27 Thus, the mechanical and thermodynamic properties are expected to be upgraded by substituting Mo into Ti 2 AlC.…”

Newly Synthesized Ta‐Based MAX Phase (Ta1−xHfx)4AlC3 and (Ta1−xHfx)4Al0.5Sn0.5C3 (0 ≤ x ≤ 0.25) Solid Solutions: Unravelling the Mechanical, Electronic, and Thermodynamic Properties

“…[ 74 ] The equations used to calculate A B and A G can be found elsewhere. [ 34 ] Table 4 shows that the anisotropy is higher in compressibility than in shear for all compositions.…”

“…A considerable improvement in compressive strength has already been reported for (Ti 1− x V x ) 2 AlC [ 29 ] and Ti 2 AlC 1− x N x . [ 30 ] Similar prospects motivate researchers to investigate other MAX phase solid solutions: (Zr,Nb) 2 (Al,Sn)C, [ 31 ] (Zr,Ti) 2 (Al,Sn)C, [ 32 ] (Zr 1− x Ti x ) 2 AlC, [ 33,34 ] (Zr,M) 2 AlC[M = Cr, Ti, or Mo] and Zr 2 (Al,A)C [A = S, As, Sn, Sb, and Pb], [ 35,36 ] (Zr,Ti) 3 AlC 2 , [ 37 ] and (Ti 1− x , Mo x ) 2 AlC. [ 38 ] Moreover, Naguib et al [ 39 ] synthesized the solid solutions (Ti 0.5 V 0.5 ) 3 AlC 2 , (Nb 0.5 V 0.5 ) 2 AlC, (Nb 0.5 V 0.5 ) 4 AlC 3 , and (Nb 0.8 Zr 0.2 ) 2 AlC and have listed 60 known solid solutions till date.…”

“…Moreover, A (Al, Ga, Ge, Si, etc.) layers are also sandwiched in between the M and X sheets [ 11 ] and the hybridization between M‐d and A‐p states leads to a comparatively weaker covalent bonding [ 34 ] compared to the MX covalent bonding. In the current case, Hf is substituted for Ta, which has one less valence electron than Ta.…”

“…The electronic properties, such as the band structure, density of states, and charge density mapping (CDM) are helpful to explain the variation of the bonding strength within solids. [ 34 ] Thus, the first‐principles study of mechanical, electronic, and thermodynamic properties of (Ta 1− x Hf x ) 4 AlC 3 and (Ta 1− x Hf x ) 4 Al 0.5 Sn 0.5 C 3 solid solutions will provide us with better insights into the effect of Hf (for Ta) and Sn (for Al) substitutions in the titled MAX phases.…”