Structure and dielectric relaxation behavior near the MPB for Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–PbTiO3 ferroelectric ceramics

The structure and dielectric relaxation behavior of the (1 − x)Pb(Mg,Ni)1/3Nb2/3O3–xPbTiO3 (PMNN-PT with Mg/Ni=1:1) compositions close to the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO3 content (x). X-ray diffraction results demonstrate that a region with both pseudocubic and tetragonal phase lies in the composition range x = 0.30–0.36. The maximum relative permittivity of 36,000 was observed at x = 0.30 near the MPB. Three empirical relations to character the relaxor behavior were discussed respectively. The dielectric permitivities of all samples well obey the relations (1/ε)=(1/εm)+((T−Tm)2/2εmδ2) and ε(T)=exp(α−βT) in a wide temperature range above Tm, but ((1/ε)−(1/εm))1/n=((T−Tm)/C) (T>Tm) may not be the proper parameter to characterize the dielectric behavior of this system. The results reveal that the PMNNT-PT ceramics successively transform from relaxor to normal ferroelectrics with the increasing of the PT content.