Microwave dielectric properties and co-firing of BiNbO₄ ceramics with CuO substitution

The effect of CuO substitution on the sintering behavior and the microwave dielectric properties of BiNbO₄ ceramics were studied. The sintering temperatures of (Bi_1-2xCu_2x)NbO_4-x and (Bi_1-2xCu_3x)NbO₄ ceramics decrease from 930 to 850 °C with x value increasing. The size of grains increased with the sintering temperature increasing and decreased with the substitution amount increasing. The dielectric constant ε_r changes between 40 and 45 and the Qf values lie between 4000 and 8000 GHz at about frequency 5.2 GHz. The τ_f values changes between 0 and -20 ppm °C^-1 and decreases with the increasing of x value. Copper electrode was found not to penetrate the ceramic from the SEM and EDS results of the broken surface of co-fired samples.