Dielectric Relaxation and Ferroelectric Properties of PNN–PZT Ceramics with Different Ni/Nb Ratios

0.35Pb(Ni x Nb 1− x )O 3 –0.65Pb(Zr 0.39 Ti 0.61 )O 3 ( x = 1/4,1/3,1/2 and 2/3) ceramics are prepared by the conventional solid reaction method and their structure, dielectric, and ferroelectric properties are studied. All compositions show tetragonal perovskite structure and Ni 2+ segregated at grain boundaries in ceramics with high Ni/Nb ( x = 1/2,2/3). Oxygen vacancies exist in nonstoichiometric ceramics and increase with the increase in Ni/Nb. Due to the pinning effect of defects, the P–E loops become unsaturated, accompanied by a softening–hardening transition. Dielectric relaxation is detected in both PNN–PZT( x = 1/2) and PNN–PZT( x = 2/3), and the activation energies of relaxation and conduction are calculated by Arrhenius law. The results show that both grain and grain boundary contribute to dielectric relaxation which can be explained on the basis of equivalent circuit containing two parallel RC elements connected in series. The relaxation at low frequency is induced by dipoles concentrating on the grain boundary while the relaxation at high frequency is attributed to the first ionization of oxygen vacancies in the grain.