Relationship Between Dielectric Relaxation Behavior and B-site Ordering of Lead Magnesium Niobate Ferroelectric Ceramics

The mechanism of the B-site ordering and disordering in Lead Magnesium Niobate (PMN)was examined by using both heat treatment and La-doped methods. The B--site structural orderingcharacteristics were exposed by X-ray diffraction (XRD), selected area electron diffraction (SAED)and high-resolution electron microscopy (HREM). The reason of the pyrochlore phase presentingwith the La-doped increased was studied. Based on the analysis of dielectric properties, theincrease in the degree of diffuse phase transition (DPT) in annealed and La-doped PMN observedwas interpreted as the Mg2+:Nb5+ = 1: 1 nonstoichiometric short-range ordered domain accompaniedwith the segregation of the Nb5+ in the disordered area. Furthermore, it was demonstrated thatthe kinetic mechanism of the ordering micro-domain growing was ion diffusion equilibrium by theeffects of the heat treatment on DPT properties of the various amounts of La-doped.