Electronic band structure of ferroelectric SrBi2Ta2O9

Abstract

The electronic band structures of both the ferroelectric and paraelectric phases of SrBi2Ta2O9 (SBT) were calculated, by first-principle methods. We find that the band gap in the ferroelectric phase increases by 0.7 eV, compared with the paraelectric phase. The edges of the valence band and the conduction band are mainly derived, respectively, from Bi 6s and O 2p states, and from Ta 5d and Bi 6p states. The partial Bi–O covalency indirectly strengthens the Ta–O hybridization, favoring stabilization of the ferroelectric phase. We attribute the SBT fatigue-free property to weak pinning of its domains by the trapped centers formed by both Bi+3 at the top of the valence band and Ta+5 at the bottom of the conduction band, and the high nonlinear refractive index in SBT to a large contribution from Ta 5d states.