Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics

The B2O3 added Ba(Zn1/3Nb2/3)O3 (BBZN) ceramic was sintered at 900 °C. BaB4O7, BaB2O4, and BaNb2O6 second phases were found in the BBZN ceramic. Since BaB4O7 and BaB2O4 second phases have an eutectic temperature around 900 °C, they might exist as the liquid phase during sintering at 900 °C and assist the densification of the BZN ceramics. Microwave dielectric properties of dielectric constant (ɛr) = 32, Q × f = 3500 GHz, and temperature coefficient of resonance frequency (τf) = 20 ppm/°C were obtained for the BZN with 5.0 mol% B2O3 sintered at 900 °C for 2 h. The BBZN ceramics were not sintered below 900 °C and the microwave dielectric properties of the BBZN ceramics sintered at 900 °C were very low. However, when CuO was added, BBZN ceramic was well sintered even at 875 °C. The liquid phase related to the BaCu(B2O5) second phase could be responsible for the decrease of sintering temperature. Good microwave dielectric properties of ɛr = 36, Q × f = 19,000 GHz and τf = 21 ppm/°C can be obtained for CuO doped BBZN ceramics sintered at 875 °C for 2 h.