First-principles study of phase transition and structural properties of AlAs

We have investigated the phase transition and structural properties of AlAs in three crystallographic structures, i.e., B3 (zinc blende), B1 (rocksalt), and B8 (nickel arsenide), at high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory (DFT). For B8 structure, it is found that the c/a ratios kept nearly constant (∼0.2% fluctuation) corresponding to V/V0 ∼ 0.7–1.05 (V is the primitive cell volume and V0 is the experimental equilibrium volume of B3 structure), which is in full agreement with experiment, but the c/a ratios increase linearly with the values of V/V0 decreasing corresponding to V/V0 ∼ 0.4–0.7. This indicates under low pressure the compression along c-axis and a-axis is the same, but the compression along c-axis is more difficult than along a-axis under higher pressure. Based on the condition of equal enthalpies AlAs is found to undergo a structural phase transition from B3 to B8 at 5.34 GPa, in agreement with the experimental value of 7 ± 5 GPa, and is speculated to undergo the B3–B1 transition at 6.24 GPa.