First-principles study of the structural, electronic and elastic properties of transition metal borides Ru3BA (A = V, Nb and Ta) compounds

In this paper, based on the first principles of density functional theory, we investigated the structure, phonon spectrum, magnetism, electronic structure, and elastic properties of cubic antiperovskite borides Ru₃BA (A = V/Nb/Ta). The lattice constants of Ru₃BA (A = V/Nb/Ta) calculated using the GGA functional are 4.01 Å, 4.06 Å, and 4.06 Å, respectively. The phonon spectrum calculations reveal that Ru₃BNb and Ru₃BTa have no imaginary frequencies, indicating that these two materials are thermodynamically stable. Although a small imaginary frequency exists in the phonon spectrum of Ru₃BV, its elastic constants meet the Born-Huang stability criterion, suggesting that Ru₃BV also has structural stability. The band structure analysis shows that Ru₃BA (A = V/Nb/Ta) are all metallic. The elastic constant data indicate that Ru₃BA (A = V/Nb/Ta) exhibit elastic anisotropy. Their Poisson’s ratio values are all 0.23, indicating that they are brittle materials. The magnetic moment calculations for Ru₃BA (A = V/Nb/Ta) are −0.11 μB, 0.29 × 10⁻⁸ μB, and −0.32 × 10⁻⁹ μB, respectively, indicating that Ru₃BV is a ferromagnetic material, while Ru₃BNb and Ru₃BTa are paramagnetic materials. Ru₃BA (A = V/Nb/Ta) not only possesses high hardness (21.17 GPa, 21.23 Gpa, and 22.09 Gpa, respectively), high bulk modulus (245.03 Gpa, 262.79 Gpa, and 272.72 Gpa, respectively), and high shear modulus (162.41 Gpa, 169.81 Gpa, and 177.55 Gpa, respectively), but also exhibits good thermal and chemical stability. Additionally, it has a certain degree of metallic properties, showing potential as a transition metal boride thin-film material. On the other hand, Ru₃BA (A = V/Nb/Ta) has good thermal stability and a high machinability index (1.89, 1.84, and 1.81, respectively), and is expected to have good application value in the mechanical fields such as cutting and grinding of ferrous metals.