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 secondary phases were found in the BBZN ceramic. Since BaB4O7 and BaB2O4 secondary 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 (epsilonr) = 32, Qxf = 3500 GHz, and temperature coefficient of resonance frequency (tauf) = 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. When CuO was added, BBZN ceramic was well sintered even at 875 C. The liquid phase related to the BaCu(B2O5) secondary phase could be responsible for the decrease of sintering temperature. Good microwave dielectric properties of epsilonr = 36, Qxf = 19000 GHz and tauf = 21 ppm/C can be obtained for CuO-doped BBZN ceramics sintered at 875 C for 2 h. 13 refs.