Pressure-driven changes in electronic structure of BiCoO<SUB>3</SUB>

Using first-principles density functional theory based calculations, carried out on the recently measured crystal structure data [ K. Oka et al. J. Am. Chem. Soc. 132 9438 (2010)], we study the changes in the electronic structure of BiCoO3 between the ambient-pressure condition and the high-pressure condition. Our study shows that the application of high pressure drives the high-spin-to-low-spin transition at the Co site. We find that the finite mixing of a Bi lone pair with O p drives the GdFeO3 type of orthorhombic distortion at high pressure, as opposed to previously predicted cubic or tetragonal symmetry of the high-pressure phase. This orthorhombic distortion gives rise to semiconducting behavior in contrast to previously predicted metallic or semimetallic behavior. Our study provides justification for the drop in resistivity on increasing pressure, as observed experimentally