Crossover from glassy to inhomogeneous-ferroelectric nonlinear dielectric response in relaxor ferroelectrics

The temperature dependence of the dielectric nonlinearities in a PMN single crystal and in 9/65/35 PLZT ceramics has been determined by measuring the first and third harmonic response as well as the dielectric behavior as a f unction of the de electric field. In zero field a paraelectric-to-glass, an d, in a high enough de field, a glass-to-ferroelectriclike: crossover in th e temperature dependence of the nonlinear response have been observed. Both crossovers agree with the predictions of the spherical random-bond-random- field model. Relaxors thus undergo in zero field a transition to a spherica l glass, while above the critical field a transition into a ferroelectric s tate occurs.