Microwave ceramics Ba5Nb4O15 and Sr5Nb4O15 prepared by a reaction-sintering process

Ba5Nb4O15 (BN) and Sr5Nb4O15 (SN) microwave ceramics prepared by a reaction-sintering process were investigated. Without any calcination involved, the Nb2O5 mixture of BaCO3 and SrCO3 was pressed and sintered directly. BN and SN ceramics could be obtained after 2–6 h sintering at 1350–1500 °C. A density 6.13 g/cm3 (97.3% of theoretical value) was obtained in BN for 4 and 6 h sintering at 1450 °C. The sintering temperature was 200 °C lowered with the addition of 1 wt.% CuO. For SN, low densification 86.9% was obtained at 1500 °C and became dense with 96% of the theoretical density at 1430 °C after 1 wt.% CuO was added. Dielectric constants 39.5 and 38.1 could be obtained in BN and SN. Q × f values 22,700 GHz at 7.2 GHz and 10,500 GHz at 7.47 GHz are observed in BN and SN.