Low-fired (PbCa) (FeNb) O3 ceramics for multilayer microwave filter applications

The microwave ceramics with compositions of Me-substituted (Pb0.45Ca0.55){[(Fe0.5Nb0.5)0.9Sn0.1]1−xMex}O3 (Me=Ti, Mn; x=0∼0.9) were prepared by solid state reaction method. A small amount of low-melting compound in Bi2O3–LiF system was added to lower the sintering temperature of the microwave ceramics. Bi2O3–LiF (5 wt.%) addition can lower the sintering temperature to lower than 950 °C. The phase, microstructure and dielectric properties were investigated with XRD, SEM and impedance analyzer. (Pb0.45Ca0.55){(Fe0.5Nb0.5)0.9Sn0.1}O3 ceramics with dielectric constant values (εr) of 89 and quality factor (Q=1/tan δ) of 1578 at 500 MHz can be obtained when the sintering temperatures are in the range of 950 °C. Furthermore, Ti or Mn substitution on B site in perovskite structure has significant effect on microstructure and dielectric properties. The greater the value of x, the higher the value of dielectric constant, product of quality factor and frequency (Q·f), and the size of crystal grain. Ti substitution can strongly enhance Q value. The experimental results show that samples with Ti substitution sintered at 950 °C, with x=0.1, has εr=92 Q=3702 at 500 MHz. It is promising to be applied to multilayer microwave filters, which require low sintering temperature.