Einfluß des elektrischen Feldes auf die fundamentale Absorptionskante von Bariumtitanat

The shift of the absorption edge of BaTiO₃ caused by an electric field has been measured in function of temperature and field strength. It shows a sharp maximum at the Curie pointT _C near 120°C, a linear field dependence belowT _C, and a quadratic field dependence aboveT _C. Furthermore this shift has the opposite sign to the Franz-Keldysh effect and is one or two orders of magnitude larger. This new effect is correlated with the electric polarization and is not induced by electromechanical lattice deformations. It is shown in a simple band model, that the relative displacement between the titanium and the oxygen sublattices induces an increase of the band gap, which agrees qualitatively with the experimental results.