First-principle calculations of structural, elastic and thermodynamic properties of Fe–B compounds

The structural, elastic and thermodynamic properties of FeB, Fe2B, orthorhombic and tetrahedral Fe3B, FeB2 and FeB4 iron borides are investigated by first-principle calculations. The elastic constants and polycrystalline elastic moduli of Fe–B compounds are usually large especially for FeB2 and FeB4, whose maximum elastic constant exceeds 700 GPa. All of the six compounds are mechanically stable. The Vickers hardness of FeB2 is estimated to be 31.4 GPa. Fe2B and FeB2 are almost isotropic, while the other four compounds have certain degree of anisotropy. Thermodynamic properties of Fe–B compounds can be accurately predicted through quasi-harmonic approximation by taking the vibrational and electronic contributions into account. Orthorhombic Fe3B is more stable than tetrahedral one and the phase transition pressure is estimated to be 8.3 GPa.