  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-FeB2 stabilizes by a
break up of 2D boron layers into 1D chains while oP10-FeB4 stabilizes by a
distortion of a 3D boron network. The uniqueness of these configurations gives
rise to a set of remarkable properties: oP12-FeB2 is expected to be the first
semiconducting metal diboride and oP10-FeB4 is shown to have the potential for
phonon-mediated superconductivity with a Tc of 15-20 K.
