Trends of complete anion substitution on electronic, ferroelectric, and optoelectronic properties of BiFeX3 (X = O, S, Se, and Te)

BiFeO3 is one of the most important perovskite ferroelectric materials. It is known that cation substitution in BiFeO3 can greatly modulate its fundamental physical properties for various applications. However, the role of anion substitution in BiFeO3 is still largely unknown. In this article, using first-principles calculations, we have systematically investigated the trends of electronic, ferroelectric, and optoelectronic properties of BiFeX3 as a function of complete anion evolution. Interestingly, the calculated bandgaps of BiFeX3, in the favorable G-type antiferromagnetic configuration, decrease from 3.32 eV (X = O) to 1.27 eV (X = S) to 0.75 eV (X = Se) and to 0.27 eV (X = Te) due to the enhanced Fe d and X p orbital hybridization at the bottom of the conduction band of BiFeX3, providing an insight to explore narrow bandgap ferroelectrics. Meanwhile, it is found that the value of spontaneous polarization of BiFeX3 decreases along with the increase in dipole moment from X = O to X = Te. In addition, the ferroelectric reversal barrier of BiFeX3 increases from X = O to X = Te, indicating that an increased external field is required to flip the opposite ferroelectric phases. The role of covalency of Bi–X bonds is revealed in the formation of spontaneous polarization. Furthermore, in the visible-light energy range, the increased absorption coefficient has been observed for larger anions and significant optical anisotropy has been found in different energy ranges for different BiFeX3 systems. Our work provides a fundamental understanding on the electronic, ferroelectric, and optoelectronic properties of complete anion substitution in BiFeO3.