New candidate ground states at $1:4$, $1:2$, and $1:1$ compositions are identified in the well-known Fe-B system via a combination of ab initio high-throughput and evolutionary searches. We show that the proposed $oP12\mathrm{\text{−}}{\mathrm{FeB}}_2$ stabilizes by a break up of 2D boron layers into 1D chains while $oP10\mathrm{\text{−}}{\mathrm{FeB}}_4$ stabilizes by a distortion of a 3D boron network. The uniqueness of these configurations gives rise to a set of remarkable properties: $oP12\mathrm{\text{−}}{\mathrm{FeB}}_2$ is expected to be the first semiconducting metal diboride and $oP10\mathrm{\text{−}}{\mathrm{FeB}}_4$ is shown to have the potential for phonon-mediated superconductivity with a $T_c$ of 15–20 K.

• Received 20 April 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.217003