ORDERING IN LEAD IRON TUNGSTATE RELAXOR CERAMICS

The ordering behavior of sodium doped lead iron tungstate ceramics, Pb 1-xNax[Fe(2-x/3) W(1 + x/3]O3), was investigated together with their d ielectric properties. The I:I type ordering of iron and tungsten catio ns, on the B sites, was evidenced by {h + 1/2, k + 1/2, 1 + 1/2} super lattice reflections in both X-ray and transmission electron microscopy diffraction. The ordering degree increases with Na content when Na le ss than or equal to 8 at% and decreases when Na>8 at%. Besides the per ovskite PFW phase, a second phase, PbWO4, was observed in Na doped PFW ceramics and its amount increases with increasing Na content. The die lectric permittivity decreases with the increase in the Na content, wh ile the diffuseness increases. It is suggested that the substitution o f Na+ for Pb2+ leads to a decrease in the charge imbalance between ord ered and disordered regions, enhancing the ordering of PFW ceramics. T he competition between the enhancement of ordering and the formation o f the PbWO4 phase is suggested to be responsible for the decrease of o rdering, when Na > 8 at%. (C) 1998 Elsevier Science Limited. All right s reserved.