MECHANISM OF FORMATION OF PEROVSKITE PHASE AND DIELECTRIC-PROPERTIES OF PB(ZN,MG)(1/3)NB2/3O3 CERAMICS PREPARED BY COLUMBITE PRECURSOR ROUTES

Abstract

The mechanism of formation of the perovskite phase and the dielectric properties of Pb(Zn,Mg)(1/3)Nb2/3O3 (PZMN) ceramics were examined using two different types of columbite precursors, (Mg,Zn)Nb2O6 (MZN) and MgNb2O6 + ZnNb2O6 (MN + ZN). The formation of perovskite phase in the PbO + MN + ZN system is characterized by an initial rapid formation of Mg-rich perovskite phase, followed by a sluggish formation of Zn-rich perovskite phase. On the other hand, due to the formation of pyrochlore phase of mixed divalent cations Pb-2-x(Zn,Mg)(y)Nb2-yO7-x-3y/2, the pyrochlore/perovskite transformation in the PbO + MZN system proceeded uniformly with a spatial homogeneity. Further analysis suggested that the formation of perovskite phase is a diffusion-controlled process. The degree of diffuseness of the rhombohedral/cubic phase transition (DPT) is higher in the PbO + MN + ZN system than in the PbO + MZN specimen for T > T-max (temperature of the dielectric permittivity maximum), indicating a broadened compositional distribution of the B-site cations in the PbO + MN + ZN system.