Exploring the real ground-state structures of W3Si silicides from first-principles calculations

Abstract The transition metal silicide W3Si was suggested to be a promising candidate for ultrahigh-temperature materials due to its good strength and ductility. However, the crystal structure of W3Si still remains unclear. Using an unbiased structure searching method, we explored the ground-state structures of W3Si up to 200 GPa. Two new tetragonal phases, P4/nmm and I-42m, are found to be energetically more favorable than the previous proposed cubic phase even at zero pressure. Electronic structure analysis reveals that both the predicted phases are metallic, and the W-5d states of which are mostly responsible for bond formations. Compared with the cubic W3Si, stronger W-Si covalent bonds are formed in the two predicted phases. The P4/nmm phase has a large shear modulus G, indicating a strong shear deformation resistance. The Vickers hardness of P4/nmm phase is larger than that of the I-42m phases. In addition, the P4/nmm phase shows slightly brittle behavior, while I-42m phase exhibits good ductility. Furthermore, the two predicted phases show isotropy character. The stress-strain calculations reveal that the ideal strengths of P4/nmm and I42-m phases are 19.6 and 12.1 GPa, respectively.