Influence of chemical bonding and magnetism on elastic properties of the A2MB2 borides (A = Nb, Ta; M = Fe, Ru, Os) from first-principles calculations

• Computation of structural variations in A2MB2 phases.
• Ta2FeB2 predicted to order antiferromagnetically.
• Chemical bonding helps predict bulk moduls trend.
• Nb2FeB2 and Ta2FeB2 predicted as hard and brittle.
• Nb2MB2 and Ta2MB2 (M = Ru, Os) should be hard and ductile.

The elastic properties of A2FeB2 (A = Nb, Ta, Mo2FeB2-type structure) and their higher homologues A2OsB2 and the predicted “A2RuB2” (both with Nb2OsB2-type structure) have been investigated within the density functional theory (DFT) framework. Furthermore, the influence of magnetism, bonding and electronic structure on the elastic properties in the A2MB2 series (A = Nb, Ta; M = Fe, Ru, Os) was studied. Ta2FeB2 is predicted to order antiferromagnetically just like Nb2FeB2 and Mo2FeB2. Magnetism affects the elastic properties of both Nb2FeB2 and Ta2FeB2 in a similar manner, but different from Mo2FeB2. We predict the ternary A2MB2 (A = Nb, Ta; M = Ru, Os) diborides to have comparable mechanical properties as the binary hard and ultraincompressible diborides RuB2 and OsB2. In general in these ternary diborides, the bulk modulus is heavily influenced by the strength of the chemical bonding (Integrated Crystal Orbital Hamilton Population: ICOHP) while the shear modulus is mainly affected by the position of the Fermi level in the density-of-states.

Figure optionsDownload as PowerPoint slide