IMF2017

Since the first synthesis and characterizaiton of Pb(Mg,Nb)O₃, relaxor ferroelectrics have been a source of fascination for materials scientists due to their unusual properties and also due to their importance in technological applications. While they possess other unusual features, dielectric response has been the hallmark of relaxor behavior and has been the focus of most studies of relaxors. Relaxors exhibit a diffuse peak in the plot of dielectric constant versus temperature as well as a strong dependence of the dielectric constant on the frequency of the applied electric field (dispersion). Since the pioneering work of Setter and Cross, both of these properties have been shown many times to be highly sensitive to the cation arrangement in the perovskite and in our previous work we have demonstrated that a quantitative relationship exists between the B-cation disorder as expressed by the standard deviation (second moment) of the B-cation valence of the oxygen atoms and the ΔT_ε,max parameter that describes the dielectric dispersion. Nevertheless, several key question have remained unresolved. For example, it is unclear how the Vogel-Fulcher and quadratic Lorentzian expressions characterizing dispersion and diffusion emerge (are connected to) the relaxor structure and dynamics. In this work, use the recently discovered nanodomain structure of relaxors as a basis for deriving a simple and general theory of relaxor behavior and use theoretical arguments and empirical correlations to show how local structure and compositions control the relaxor dielectric response as characterized by dispersion (ΔT_ε,max) and diffusion (σ) descriptors.