Pressure-driven changes in electronic structure of BiCoO$_3$

Using first-principles DFT based calculations, carried out on the recently measured crystal structure data [Oka et.al. J.Am.Chem.Soc.132, 9438 (2010)], we study the changes in the electronic structure of BiCoO$_3$ between the ambient-pressure and the high-pressure conditions. Our study shows that the application of high pressure drives the high-spin-to-low-spin transition at the Co site. The obtained results for the ambient pressure phase shows C-type AFM alignment of Co high spins, while the electronic structure at the high-pressure phase shows the presence of a finite energy gap at E$_f$ in contrast with previously reported metallic or semimetallic character with low-spin state of Co. This semiconducting behavior in the nonmagnetic BiCoO$_3$ with LS state of Co is found to be driven by the presence of the GdFeO$_3$ type of orthorhombic distortion which arises due to finite mixing of Bi lone-pair states with O-p states, as opposed to previously predicted cubic or tetragonal symmetry of the high-pressure. The ambient pressure phase shows an order of magnitude larger energy gap arising due to the AFM alignment of Co in the high-spin state than the energy gap at the high pressure phase, explains the observed 3-order of magnitude jump in resistivity.