Fabrication of PMN and PFN ceramics by a two-stage sintering technique

Relaxor perovskite ceramics of lead magnesium niobate (PMN) and lead iron niobate (PFN) have been prepared by employing a two-step mixed oxide synthetic route, followed by the application of a two-stage sintering method. The effect of the latter on phase formation, densification behaviour, microstructure and dielectric properties of both relaxor systems is examined. Two types of pyrochlore phase are found to co-exist with the major phase in the PMN system, i.e. Pb₃Nb₄O₁₃ and Pb_1·83Nb_1·71Mg_0·29O_6·39 with an MgO inclusion. By comparison, a PbFe₈O₁₃ pyrochlore phase with an Fe₂O₃ inclusion is observed in the PFN system. The types and concentrations of phases present are found to depend upon sintering conditions. In connection with dielectric properties, a substantial dependence of the maximum values of both relative permittivity (′_r,max) and dissipation factor (tanδ_max) on sintering regime is observed. By employing optimised two-stage sintering conditions, high density ceramics with low firing temperatures and reasonable relative permittivities can be achieved in both systems.