Reversible permittivity of a photosensitive relaxor ferroelectric

The reversible permittivity of barium strontium niobate, a photosensitive relaxor ferroelectric, doped with lanthanum and cerium is investigated in the dark and under illumination with a power density of 0.22 mW/cm(2). The permittivity is measured under a combined effect of a weak ac electric field at a frequency of 1 MHz and a slowly varying periodic field E-b with an amplitude of +/- 2.3 kV/cm. It is shown that the illumination significantly increases the permittivity, changes the dependence of the permittivity on the periodic field E-b, and eliminates the possible unipolarity of the crystal, thus significantly improving the reproducibility of the permittivity during repeated measurements.