On the permittivity of barium strontium niobate, a photosensitive relaxor ferroelectric

The permittivity ? of the photosensitive relaxor ferroelectric Sr_0.61Ba_0.39Nb₂O₆ doped with La and Ce is studied both in the dark and under illumination with a power density of up to 0.22 W/cm² in the wavelength range 400–500 nm of the absorption spectrum of the crystal. The permittivity ? is measured at frequencies of 1 kHz and 1 MHz, as well as under a dc electrical bias of 2 kV/cm at different temperatures. It is found that the permittivity ? exhibits a photoinduced increase (photodielectric effect), which reaches a maximum in the temperature range of the maximum permittivity and is proportional to the illumination power density. The specific features of the observed photodielectric effect and the possible influence of the screening of random internal nonuniform electric fields by photoinduced carriers on this phenomenon are discussed.