Low-temperature sintering and microwave dielectric properties of Ba₅Nb₄O₁₅-BaNb₂O₆ mixtures for LTCC applications

The addition of B₂O₃ to Ba₅Nb₄O₁₅-BaNb₂O₆ significantly lowered the sintering temperature to ∼900 °C in comparison to ∼1250 °C for samples without B₂O₃. The presence of a B₂O₃-rich intergranular phase in the sample was observed, which was attributed to the presence of a liquid phase during sintering. The barium metaniobate, BaNb₂O₆ has two polymorphs, with orthorhombic and hexagonal forms. A major contributor to microwave dielectric properties of low-fired samples is the low temperature phase, hexagonal BaNb₂O₆. The small amount of hexagonal BaNb₂O₆ could tune τ_f of Ba₅Nb₄O₁₅. Therefore, Ba₅Nb₄O₁₅-BaNb₂O₆ with B₂O₃ can be a suitable for low-temperature cofired ceramic (LTCC), due to its reduced sintering temperature and good microwave dielectric properties: Q×f = 28 000 GHz, ε_r and τ_f are 42 and 0 ppm/°C, respectively. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.