Revealing phase relations between Fe2B7 and FeB4 and hypothetical Fe2B7-type Ru2B7 and Os2B7: first-principles calculations

Abstract

Investigation of new materials recovered using high pressure can foresee the unobservable structures and bonding of crystals. Employing first-principles calculations, we aim to provide an atomic understanding of the origin of multiple phases and mutual intergrowth for metastable iron borides. The competing FeB₄ and Fe₂B₇ in the experiment are compared by their enthalpy and structural features. The closely similar enthalpy of Fe₂B₇ + B and Fe₂B₈ (FeB₄) may explain the coexistence and tight mutual intergrowth of these two phases. The hypothetical Ru₂B₇ and Os₂B₇ are also suggested by the stability evaluations. The stable Ru₂B₇ and Os₂B₇ show an interesting metallic property and a great mechanical property due to the hybridization of metal-d and B-p orbitals and B–B covalent bonding.