Low-loss and temperature stable (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics with low sintering temperature

In this study, the Ba₃P₂O₈ and Mg₂B₂O₅ were fabricated by the solid-state reaction method separately, and the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE_01δ mode dielectric resonator method, respectively. The results revealed that the Mg₂B₂O₅ phase and Ba₃P₂O₈ phase could coexist well in the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics without formation of any new phases. The abnormal grain growth of Ba₃P₂O₈ grains was inhibited by the addition of Mg₂B₂O₅. In addition, through composition of Ba₃P₂O₈ and Mg₂B₂O₅, the temperature coefficient of resonant frequency (τ_f) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic was achieved at a sintering temperature of 920 °C, τ_{f =} −1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity ε_r = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic is a candidate LTCC material with wide application prospects.