Preparation and properties of PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 composition

Abstract

We prepared and characterized PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 stoichiometric composition. We examined microstructures, sintering behavior, and phase compositions in this system and prepared several new compositions, which have a single phase perovskite structure and a high dielectric constant (28000), by low sintering temperature (950–1020 °C). These compositions have a high electrical resistivity (1013 ohm-cm), which is about 1000 times higher than those of Pb(Fe½Nb½)O3 and Pb(Fe⅔W⅓)O3 based ceramics. The new compositions can be readily prepared into a single phase perovskite without a detectable amount of pyrochlore second phase by a simple method of mixing and calcining the constituent oxide and carbonate powders. Our dielectric measurements and XRD data establish the correlation between the decrease in dielectric constant and the presence of pyrochlore second phase. The effects of PbTiO3 dopant were quantitatively measured and our data showed that at a low (10 mole %) PbTiO3 concentration, the Curie temperature increases 6.6 °C for every mole % PbTiO3 dopant in the new compositions. The dielectric constant increases from 18000 in the undoped composition to 27 100 and 29000 by a PbTiO3 dopant concentration of 5% and 10%, respectively. The maximum dissipation factor also decreases from 0.10 in the undoped composition to 0.055 in the 10% PbTiO3 doped composition. The electrical resistivity, ρ, decreases with the PbTiO3 dopant concentration, t, following the ρ = ρ0 exp (–t/t0) relation where ρ0 ≍ (9.6 ± 0.2) × 1012 Ωcm and t0 ≃ 0.044.