First-principles calculations to investigate pressure effect on structural, elastic and thermodynamic properties of AlCu, Al2Cu and Al4Cu9

The structural, elastic and thermodynamic properties of AlCu, Al2Cu and Al4Cu9 under pressure were investigated using a first-principles approach. The volume ratio (V/V0) and equilibrium lattice constants (a/a0, b/b0 and c/c0) decreased with the increasing pressure. Al4Cu9 outperformed AlCu and Al2Cu in terms of structural stability because it has the lowest cohesive energy (ΔE). The elastic constants (Cij) showed that AlCu, Al2Cu and Al4Cu9 were mechanically stable at a pressure of 0–20 GPa. Increasing pressure enhanced the resistance to deformation. The results of Young's modulus (E) indicate that AlCu and Al4Cu9 were stiffer than Al2Cu. Based on the results of Cauchy pressure (C12–C44) and the B/G ratio, increasing pressure transformed AlCu from brittle to ductile above 15 GPa. The microhardness of AlCu (13.76 GPa) was larger than that for Al2Cu (7.78 GPa) and Al4Cu9 (9.81 GPa), and it can therefore be classified as a ‘hard material’ (Hv＞10 GPa). These results are in good agreement with experimental results. The obtained Debye temperature (θD) implied that the covalent bonds of AlCu were the strongest. The pressure and temperature had opposite effects on heat capacity at constant volume (Cv). The capability of storing or releasing heat of Al2Cu was stronger than that for AlCu and Al4Cu9.