First-Principles Study on the Stability and Electronic Properties of Bi-Doped Sr₃Ti₂O₇

The electronic and crystal structural properties of Bi-doped Sr₃Ti₂O₇ are studied using the first principles density functional theory (DFT) based on pseudopotentials basis and plane-wave method. Our results show that the formation energy of Bi doping in Site-1 and Site-2 of Sr₃Ti₂O₇ increases with increasing doping concentration. And at the same doping concentration, the formation energy of Bi doping in Site-2 is lower than that in Site-1. The undoped Sr₃Ti₂O₇ is found to be an insulator and its Fermi level stays at the top of the valence band. While the Fermi level of the Bi-doped Sr₃Ti₂O₇ moves into the bottom of conduction band, the system undergoes an insulator-to-metal phase transition. Furthermore, our calculation results demonstrated that the Fermi level of the Bi-doped Sr₃Ti₂O₇ goes deeper into the bottom of conduction band with increasing doping concentration.