Evidence of random electric fields in the relaxor-ferroelectric Sr0.61Ba0.39Nb2O6

We present strong evidence of the existence of quenched random electric fields in relaxor ferroelectrics by investigating the aging in ferroelectric hysteresis loops under light illumination. The temporal behaviour of ferroelectric domains under external electric fields and light illumination is measured in cerium-doped strontium-barium-niobate crystals using quasistatic surface charge detection. The aging, caused by electric pinning centres which hinder domain wall motion, leads to a decrease in domain wall mobility. Raising the sample conductivity by illumination eliminates the pinning centres and fully restores the polarization dynamics.