Microwave dielectric properties of low-loss (Zn1−xCox)3Nb2O8 ceramics for LTCC applications

Abstract

The phase relation, crystal structure and microwave dielectric properties of (Zn1−xCox)3Nb2O8 ceramics were investigated. The limit of (Zn1−xCox)3Nb2O8 solid solutions was approximately x=0.4. With an increasing x, the corrected dielectric constant decreased and the temperature coefficient of resonant frequency (τf) increased. The τf value is strongly dependent on the tilting of the oxygen octahedral, which can be evaluated by the B-site bond valence. However, a tremendous loss reduction can be achieved by a small amount of Co substitution due to the increase in relative density and packing fraction. The B2O3 and CuO addition can effectively lower the sintering temperature of (Zn0.95Co0.05)3Nb2O8 without seriously deteriorating the dielectric properties. For LTCC applications, the 4wt% B2O3–CuO doped (Zn0.95Co0.05)3Nb2O8 ceramic sintered at 930°C is a good choices because of its excellent dielectric properties (ɛr∼20.75, Q×f∼105,000GHz and τf∼−83.7ppm/°C) and the chemical compatibility with silver.