The microwave dielectric properties and the microstructures of Bi(Nb, Ta)O4 ceramics

The microwave dielectric properties and the microstructures of (1 - x)BiNbO4-xBiTaO4 ceramics (x = 0, 0.15, 0.2, 0.4, and 0.6) doped with 0.5 wt% CuO ale investigated. Ta is substituted for Nb in order to adjust the temperature coefficient of the resonant frequency (tau(f)) and improve the quality factor (Q). All BiNb(1-x)TaxO4 compositions can be sintered to achieve a 96% theoretical density below 960 degrees C. The sintering temperatures of BiNb(1-x)TaxO4 increase with increasing of x values. The dielectric constants (epsilon(r)) of all compositions saturate at 44-45 in spite of the Ta content. Q x f values of 13000-22000 (GHz) are obtained for all compositions when the sintering temperatures are in the range of 920-940 degrees C. By increasing the amount of the doped Ta, the temperature coefficient of the resonant frequency tau(f) can be adjusted from a positive value of +15 ppm/degrees C to a negative value of -30 ppm/degrees C. The BiNb(1-x)TaxO4 ceramics can be applied to multilayer microwave devices with low sintering temperatures.