Microstructural evolution and electrical properties of base-metal electroded BaTi4O9 materials with B-Si-Ba-Zn-O glass system

Barium titanate material systems are the basic microwave dielectrics attracting particular interests and subject to many researches due to lots of intriguing properties, such as, its high temperature stability, low loss, high dielectric constant etc. at microwave range. However, BaTi₄O₉ and Ba₂Ti₉O₂₀ ceramics usually need very high sintering temperatures (~1300°C and above) to achieve sufficient density. The present work attempts to investigate the microstructures and corresponding electric properties of low temperature co-fired BaTi₄O₉ microwave dielectric ceramics with copper electrode and B-Si-Ba-Zn-O glass in reducing atmosphere. Experimental results show that specimens of BaTi₄O₉ ceramics with various glass compositions and Cu-electrode exhibit different colors and can be attributed to glass diffusivity and reaction with Cu element during sintering. Glass composition plays an important role of the mass transportation of glass. B₂O₃/SiO₂ ratio determines glass viscosity and BaO/ZnO ratio contributes to wettability of glass with BaTi₄O₉ ceramics. In x-ray diffraction patterns, we can observe different Ba-Ti-O phases with various Ba/Ti ratio. Ba₄Ti₁₃O₃₀ may form when the BaO content in glass is too high (BaO/ZnO ratio is greater than 2). Instead, the BaTi₆O₁₃ appears as the content of BaO is low, such as BaO/ZnO ratio is smaller than 0.75. Both extreme conditions degrade the electrical properties of materials. Appropriate composition of glass not only improves material density during sintering, but also enhances phase stability of dielectrics and electrical properties.