The Effect of Alloying Elements on the Structural Stability, Mechanical Properties, and Debye Temperature of Al3Li: A First-Principles Study

Abstract

The structural stability, mechanical properties, and Debye temperature of alloying elements X (X = Sc, Ti, Co, Cu, Zn, Zr, Nb, and Mo) doped Al3Li were systematically investigated by first-principles methods. A negative enthalpy of formation ΔHf is predicted for all Al3Li doped species which has consequences for its structural stability. The Sc, Ti, Zr, Nb, and Mo are preferentially occupying the Li sites in Al3Li while the Co, Cu, and Zn prefer to occupy the Al sites. The Al–Li–X systems are mechanically stable at 0 K as elastic constants Cij has satisfied the stability criteria. The values of bulk modulus B for Al–Li–X (X = Sc, Ti, Co, Cu, Zr, Nb, and Mo) alloys (excluding Al–Li–Zn) increase with the increase of doping concentration and are larger than that for pure Al3Li. The Al6LiSc has the highest shear modulus G and Young’s modulus E which indicates that it has stronger shear deformation resistance and stiffness. The predicted universal anisotropy index AU for pure and doped Al3Li is higher than 0, implying the anisotropy of Al–Li–X alloy. The Debye temperature ΘD of Al12Li3Ti is highest among the Al–Li–X system which predicts the existence of strong covalent bonds and thermal conductivity compared to that of other systems.

A first-principles study on the site occupancy behavior of transition metals in L12-Al3Li phase

“…Our site preference results are also in good agreement with the previous DFT study from Ref. [26], however, according to our calculated transfer energy, Co shows no site preference in stoichiometric Al 3 Li, while Co has a Al-sublattice preference in the study of Ref. [26] by formation enthalpies of alloys.…”

“…For example, our calculated formation enthalpy of a Sc atoms locating at Li site of L1 2 -Al 3 Li is −0.111eV, while the literature result [26] is −0.180 eV, namely, there is a discrepancy of 0.07 eV/atom. The reason for the discrepancy is that the formation enthalpies in [26] are obtained by a 16-atom [1×1×4] L1 2 -Al 3 Li supercell, meaning that there is a concentration-dependent formation enthalpy discrepancy between our calculations for Al 3 LiX alloy, namely, x X =1/108 in this study and x X =1/16 in the [26] make this discrepancy. Moreover, the interactions between defects in neighboring [1×1×4] L1 2 -Al 3 Li supercells may induce such energy discrepancies [43].…”

“…Generally, a lower value of the formation enthalpy means the material is more stable. We have also compared our calculated formation enthalpies to literature data [26], which shows a good agreement in the formation enthalpies of X locating at Al site or Li site. However, one also notices the large discrepancies between ours and the literature results.…”

“…[26], however, according to our calculated transfer energy, Co shows no site preference in stoichiometric Al 3 Li, while Co has a Al-sublattice preference in the study of Ref. [26] by formation enthalpies of alloys. It has been show that the formation enthalpies DH X Al and DH X Li are insufficient to determine the site preference of ternary alloying elements, which is also determined by the formation enthalpies of the intrinsic point defects (Vac Al , Vac Li , Li Al , Al Li ) in binary L1 2 Al 3 Li alloys [35,46].…”

“…However, in order to identify the effect of alloying elements on the improvement of the thermodynamic and mechanical properties of Al 3 Li, knowing of the solute elements site occupancy behaviour in ordered L1 2 Al 3 Li is of great importance. Despite the fact that the mechanical and thermodynamic properties [16][17][18][19][20][21][22][23][24][25] as well as the site preference behaviour [26] of a list of elements in L1 2 -Al 3 Li have been investigated previously in the literature, there is no systematic calculation of alloying elements site occupancy behaviour for the whole transition metals in L1 2 -Al 3 Li phase. Particularly, Tian et al [26] have studied the site preference of a list of alloying elements (8 elements) in L1 2 Al 3 Li by using first-principles calculations, they have used the enthalpy of formation of alloyed L1 2 Al 3 Li to predict the 0K site preference of solute.…”