Phase evolution and electrical properties of copper-electroded BaTi4O9 materials with BaO–ZnO–B2O3–SiO2 glass system in reducing atmosphere

BaTi4O9 (BT4) microwave dielectric ceramics using a copper electrode and containing 10 wt% BaO–ZnO–B2O3–SiO2 (BZBS) glass frit were sintered under reducing atmosphere at 950 °C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO2 and ZnO/SiO2 ratios of BZBS glasses. Experimental results show that the BaO/SiO2 ratio contributes to wettability of glass with BaTi4O9 ceramics, and ZnO/SiO2 ratio determines the densification of BaTi4O9 ceramics. The different Ba–Ti–O and Ba–Cu–O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba4Ti13O30 and Ba2Cu3O5+X may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO3 and Ba2Cu3O5+X phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO2 ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.