Quasi-static loops of the dielectric hysteresis for a photosensitive relaxor ferroelectric crystal in the temperature range of the diffuse phase transition

This paper reports on the results of an investigation into the dielectric hysteresis loops of La-and Ce-doped barium strontium niobate, a photosensitive relaxor ferroelectric, both in the dark and under illumination with an intensity of 0.22 mW/cm². Measurements are performed in a quasi-static electric field at a frequency of 5 × 10^?4 Hz for different temperatures in the range of the diffuse phase transition. Illumination increases the hysteresis loop amplitude. The amplitude and the coercive field decrease under heating, and the difference between the loops measured for illuminated and unilluminated crystals disappears gradually as the temperature of the maximum in the permittivity is approached. The experimental results are not in conflict with the assumption that random internal relaxor fields are screened by photoinduced carriers.