Multilayer capacitor ceramics in the PMN-PT-BT system: Effect of MgO and 4PbO center dot B2O3 additions

Coexistence of pyrochlore phase is one of the major problems in the preparation of lead magnesium niobate (PMN) based perovskites as it leads to deterioration of the dielectric and piezoelectric properties. Although the columbite precursor method substantially reduces the formation of pyrochlore phase, the success of this process depends on various process conditions such as reactivity of MgO, level of mixing or grinding, control of PbO volatility and reversibility of the reaction. Compositions in the system (1 - x)[(1 - y)PMN yPT]xBT (where PT = PbTiO3 and BT = BaTiO3) were prepared by the columbite route. Results show that addition of excess MgO and 4PbO . B2O3 glass before sintering not only eliminates the pyrochlore phase completely but also produces a series of ceramics with low firing temperature, very high dielectric constant, low dissipation factor, high d.c. resistivity and extremely low temperature coefficient of capacitance (TCC). The unusually low TCC values make these high K dielectrics suitable for application in multilayer ceramic capacitors having EIA specifications Y5P, Y5R and Y5S.