Optical and dielectric investigations in SBN:Ce

Abstract

In Sr0.61Ba0.39Nb2O6 (SBN) doping with Ce enhances the photorefractive properties [1]. Many details and microscopic properties of the centers and their interaction with light are not yet sufficiently understood. Fourier-spectroscopy in a wide spectral range from UV to the FIR was employed to investigate the absorption spectra and their change under intensive Ar+-laser light illumination. At about 2200 cm(-1) transitions due to Ce3+ spin orbit split 4f-states display at low temperatures characteristic light induced changes indicative of the Ce3+-oxidation state. A broadband polaronic Nb4+-absorption at about 1.6 mu m, known from reduced SBN crystals, also appears under Ar+-laser illumination at low temperature. Light induced charge transfer processes lead to absorption changes, which can be explained consistently on the basis of a simplified model involving Ce3+/4+-centers and polaronic Nb4+-centers [6]. In addition to the ferroelectric relaxer transition at T = 350 K (4/mmm to 4 mm) a further phase transition (4 mm to m) [7] at low temperature (T approximate to 90 K) has been confirmed by dielectric and pyroelectric measurements. Both phase transition temperatures are shifted to lower values with increasing cerium content.