Cr concentration driving the structural,mechanical, and thermodynamic properties of Cr-Al compounds from first-principles calculations

Cr-Al binary compounds are regarded as the potential high-temperature structural materials. However, the structure and important properties of Cr-Al compounds are not completely unclear. Here, we report on the influence of Cr concentration on the structural, mechanical, and thermodynamic properties of Cr-Al compounds by using the first-principles calculations. Four novel Cr-Al compounds, Cr₃Al₈ with monoclinic structure (C2/m), Cr₃Al₅ with hexagonal structure (P63mc), Cr₂Al₃ with tetragonal structure (I4/mmm), and Cr₃Al with cubic structure (Pm-3 m), are predicted. The calculated elastic modulus of Cr-Al compounds gradually increases with increasing Cr concentration. Compared to other Cr-Al compounds, our predicted Cr₃Al with cubic structure exhibits a strong deformation resistance and high hardness due to symmetrical Cr Al bonds. However, the Debye temperature of Cr₇Al₃ is larger than that of other Cr-Al compounds. The calculated phonon density of state shows that the high-temperature thermodynamic properties of Cr-Al compounds are attributed to the vibration of Al atom and Cr Al bond.