Co-substituted BiFeO3: electronic, ferroelectric, and thermodynamic properties from first principles (original) (raw)

BiFeO3 is a multiferroic solid that is of interest as a potential photovoltaic and photocatalytic material. The ferroelectric character might enhance carrier separation, but the efficiency is limited by a wide electronic bandgap. With the motivation of finding routes to engineer the bandgap and the band structure, we have investigated the thermodynamic, electronic and ferroelectric properties of BiCoxFe1 xO3 solid solutions, with 0 < x < 0.13, using density functional theory. We show that the bandgap can be reduced from 2.9 eV to 2.1 eV with cobalt substitution, while simultaneously enhancing ferroelectric behaviour: a large spontaneous polarisation is predicted for the Co-substituted system, due to notably larger Born effective charge of Co compared to Fe cations. We discuss the interaction between Co impurities, which is strongly attractive and would drive the aggregation of Co, as evidenced by Monte Carlo simulations, at temperatures of interest. Phase separation into a Co-...