Universal domain wall dynamics in ferroelectrics and relaxors

The ac susceptibility of the uniaxial relaxor strontium barium niobate, Sr-0.61 Ba0.39Nb2O6, the quantum ferroelectric strontium titanate, (SrTiO3)-O-18, and the periodically, poled superionic ferroelectric potassium titanyl phosphate, KTiOPO4, reveals different modes in dependence on the frequency. Relaxation of domain wall segments and creep, respectively, are connected by a dynamical transition with universal properties as described by the scaling theory of domain walls in random media. The depinning frequency obeys Arrhenius activation, and dielectric non-linearity sets in when entering the creep regime from high frequencies.