Dielectric relaxation and phase transition behavior of (1–x)Pb(Zn_1/3Nb_2/3)O₃-xBaTiO₃ binary solid solutions

Dielectric relaxation and phase transition behaviors in (1–x)Pb(Zn_1/3Nb_2/3)O₃-xBaTiO₃ (PZN-BT) binary solid solutions have been systematically studied in this paper. All the compositions display a pure pseudo-cubic perovskite structure. As the BT contents increase from 10 mol% to 70 mol%, the phase transition peak becomes broader and broader, accompanying with decreases of ɛ_m (the maximum dielectric permittivity) and T_m (the temperature corresponds to the ɛ_m). Nevertheless, an abnormal increase of ɛ_m and T_m occurs when the BT contents exceeds 70 mol%, forming a “U” shaped curve of the compositional dependence of ɛ_m and T_m. Moreover, it is indicated from the new glass model fitting results that the characteristic parameter p, which represents the degree of relaxation, also shows a similar “U” shaped variation curve. Similarly, as shown in polarization-electric field loops, both remnant polarizations (P_r) and coercive fields (E_c) display the “U” shaped curve as the BT content changes from 10 mol% to 80 mol%. Finally, according to the similar variation of these key parameters mentioned above, a polarization mismatched model, which describes the destruction and reestablishment of the long range order arrangement in solid solutions composed of two kinds of ferroelectrics, is proposed to illustrate the underlying mechanism. In this PZN-BT system or other similar ABO₃-type perovskite relaxors, the competition between the A-O and B-O coupling plays an important role to form the “U” shaped evolution of these key parameters.