The effects of Al and Ti additions on the structural stability, mechanical and electronic properties of D8m-sStructured Ta₅Si₃

Abstract

In the present study, the influence of substitutional elements (Ti and Al) on the structural stability, mechanical properties, electronic properties and Debye temperature of Ta₅Si₃ with a D8m structure were investigated by first principle calculations. The Ta₅Si₃ alloyed with Ti and Al shows negative values of formation enthalpies, indicating that these compounds are energetically stable. Based on the values of formation enthalpies, Ti exhibits a preferential occupying the Ta⁴b site and Al has a strong site preference for the Si⁸h site. From the values of the bulk modulus (B), shear modulus (G) and Young’s modulus (E), we determined that both Ti and Al additions decrease both the shear deformation resistance and the elastic stiffness of D8m structured Ta₅Si₃. Using the shear modulus/bulk modulus ratio (G/B), Poisson’s ratio (υ) and Cauchy’s pressure, the effect of Ti and Al additions on the ductility of D8m-structured Ta5Si3 are explored. The results show that Ti and Al additions reduce the hardness, resulting in solid solution softening, but improve the ductility of D8m-structured Ta₅Si₃. The electronic calculations reveal that Ti and Al additions change hybridization between Ta-Si and Si-Si atoms for the binary D8m-structured Ta₅Si₃. The new Ta-Al bond is weaker than the Ta-Si covalent bonds, reducing the covalent property of bonding in D8m-structured Ta5Si3, while the new strong Ti⁴b-Ti⁴b anti-bonding enhances the metallic behavior of the binary D8m-structured Ta₅Si₃. The change in the nature of bonding can well explain the improved ductility of D8m-structured Ta₅Si₃ doped by Ti and Al. Moreover, the Debye temperatures, ΘD, of D8m-structured Ta₅Si₃ alloying with Ti and Al are decreased as compared to the binary Ta₅Si₃