Role of perovskite PMN in phase formation and electrical properties of high dielectric Pb[(Mg_x, Zn_1-x)_1/3Nb_2/3]O₃ ceramics

The structural evolution of perovskite phase Pb[(Mg_xZn_1-x)_1/3Nb_2/3]O₃ (abbreviated to PZMN) was found to be highly dependent on its precursors' strong tendency of forming pyrochlore phase in the mixture of raw materials. Three major pyrochlore compositions, Pb₂Nb₂O₇, Pb₃Nb₂O₈ and Pb₃Nb₄O₁₃, were characterized and analyzed to understand their roles in the formation of the perovskite PZMN phase. Based on phase structure evolution, a preparation method for forming high dielectric constant PZMN ceramics without using common stabilizers such as SrTiO₃ was proposed. By using pre-synthesized perovskite PMN, a Zn-rich PZMN composition with an almost 100% perovskite content and a maximum dielectric constant of 22 000 at 1 kHz is obtained. The formation mechanism of PZMN perovskite phase was also reported in this research. The pre-synthesized perovskite PMN acts as stabilizer and nuclei to initiate PZMN perovskite formation through the reaction in the PMN/ZnO interface. A ternary phase diagram of PMN-PZN-SrTiO₃ was further constructed to investigate the perovskite development and its related electrical properties.