Is Orthorhombic Iron Tetraboride Superhard?

Millimeter-sized FeB$_{4}$ bulks were synthesized under high pressure of 15 GPa and 1600 $^{\circ}$C. Multiple analysis methodologies including XRD, SEM, TEM, and Raman spectroscopy verified this new phase with an oP10 crystal structure. A relatively low hardness value of 15.4 GPa, which is consistent with both macroscopic and microscopic hardness models, excludes FeB$_{4}$ as a superhard material. Resistance and magnetization measurements do not indicate superconductivity in FeB$_{4}$for temperature as low as 2.5 K. Previously reported superconductivity in FeB$_{4}$ needs a further investigation, especially for structural imperfections, unidentified phases, and/or contaminations.