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

Barium titanate-based microwave dielectrics usually require relatively high temperatures to sinter, which prevents the use of base metals such as copper for electrodes. In this work, BaTi₄O₉ microwave dielectric ceramics co-fired with copper electrodes are made possible by adding B-Si-Ba- Zn-O glass to induce liquid-phase sintering at sufficiently low temperature and in reduced atmosphere. The microstructures and electric properties of the BaTi₄O₉ ceramics thus obtained are carefully examined and studied. Proper glass composition may significantly facilitate mass transportation in the low-temperature co-fired ceramic (LTCC) material, resulting in better densification without serious degradation of electric properties. Although the B₂O₃/SiO₂ ratio enhances the glass mobility during sintering, the BaO/ZnO ratio contributes to the chemical affinity of glass to BaTi₄O₉ ceramics. In addition, various Ba-Ti-O phases with different Ba/Ti ratios may be found in the specimen through the X-ray diffraction patterns when the BaO/ZnO ratio is varied. If the BaO/ZnO ratio is high and the glass flows easily in the material, the Ba₄Ti₁₃O₃₀ phase is formed. If the BaO/ZnO ratio is low and the glass flows easily in the material, the BaTi₆O₁₃ phase appears. We find that glass-induced Ba₄Ti₁₃O₃₀ transformation may significantly decrease Q×f values in the BT4-BSBZ materials. Therefore, the appropriate glass composition must be selected to ensure the phase stability of dielectrics to achieve the best performance possible.