Electronic structure and ferroelectricity in ${\mathrm{SrBi}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$

The electronic structure of ${\mathrm{SrBi}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ is investigated from first-principles, within the local-density approximation, using the full-potential linearized augmented plane-wave method. The results show that, besides the large $\mathrm{Ta}\mathrm{}\left(5d\right)\mathrm{}-\mathrm{O}\mathrm{}\left(2p\right)\mathrm{}$ hybridization which is a common feature of the ferroelectric perovskites, there is an important hybridization between bismuth and oxygen states. The underlying static potential for the ferroelectric distortion and the primary source for ferroelectricity is investigated by a lattice-dynamics study using the frozen-phonon approach.