The spherical random bond random field model and the relaxor to ferroelectric transition

To check whether the recently proposed SRBRF model also adequately describes the relaxer to ferroelectric transition the temperature dependence of the static dielectric constant of PMN has been fitted to the SRBRF model. The results show that in contrast to dipolar glasses the mean coupling constant J(0) is here indeed close to the root mean square variance J For E greater than or equal to E-C J(0) can therefore become bigger than J resulting in a transition from a relaxor to a ferroelectric state. The relaxor to ferroelectric cross-over in the non-linear dielectric response a(3) = chi (3)/chi (l) (4) in the form predicted by the SRBRF model for E greater than or equal to E-C has been observed in PLZT ceramics. The temperature dependence of the Edward-Anderson order parameter q has been determined via NMR in PSN in the region of the ferroelectric transition and as well shows the T-dependence predicted far J(0) > J. The relaxor to ferroelectric transition can be thus well described by the SRBRF model.