Optical properties of ferroelectric Bi4Ti3O12

We report optical properties of ferroelectric Bi4Ti3O12 based on spectroscopic ellipsometry and calculations with the recently developed density functional of Tran and Blaha. We find a close accord between the experiment and the calculated results with this functional, including the energy onset of optical transitions and the scale of the optical conductivity. The band gap is indirect, with a value of 2.9 eV, and an onset of direct optical transitions at 3.1 eV.