Abstract
Substitutional charge disorder in ferroelectrics giving rise to quenched electric random-fields (RFs) is probably at the origin of their relaxor behavior. Fluctuating polar nanoregions in the paraelectric regime are related to the spatial fluctuations of the RFs. While they destroy the ferroelectric phase transition and give rise to a glassy state in cubic relaxors like PbMg⅓Nb2/3O3, uniaxial systems like Sr1-x Ba x Nb2O6 exhibit RF Ising model behavior with non-classical critical exponents, e.g. α ≈ 0. Metastable pinned nanodomains in the ferroelectric regime are at the origin of non-Debye dielectric response, non-exponential relaxation, aging and memory effects.
Acknowledgments
Financial support by DAAD, DFG (SPP “Strukturgradienten in Kristallen”) and NATO (PST.CLG.977409) is gratefully acknowledged.