REACTION-KINETICS OF PEROVSKITE PHASE FORMATION IN LEAD ZINC MAGNESIUM NIOBATE CERAMICS

The reaction kinetics of perovskite Pb[(Zn,Mg)1/3Nb2/3]O3-SrTiO3 (PZMN-ST) phase formation vary with the phase condition of the starting materials. Basically, the reaction is controlled by a diffusion process with either a fixed number of nuclei or a constant nucleation rate. When the Pb3Nb2O8 (P3N2) phase is used as the starting material, the reaction belongs to the former. The P3N2 phase acts as a nucleation center and fixes the number of nuclei for perovskite phase formation. If PbO and Nb2O5 instead of P3N2 are used as starting materials, the nucleation center will be the pyrochlore phase Pb2Nb2O7 or P3N2 and is continuously created by the reaction of residual PbO with the formed pyrochlore Pb3Nb4O13 phase. In the final stage of PZMN formation, the reaction is mainly through diffusion of ZnO into PMN or Zn-containing PMN. The importance of the pyrochlore phase to perovskite PZMN phase formation is consequently asserted.