Low temperature sintering and microwave dielectric properties of Ba3(PO4)2–BaWO4 composite ceramics

(1−x)Ba3(PO4)2−xBaWO4 composite ceramics were prepared by cofiring mixtures of Ba3(PO4)2 and BaWO4 powders at around 1050–1150 °C. The phase assemblages, microstructures and element composition were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis, respectively. Microwave dielectric properties were measured with a network analyzer. It was found that Ba3(PO4)2 and BaWO4 coexisted after sintering at about 1100 °C/2 h. Both εr and τf of the composite ceramics decreased linearly with the increase of BaWO4 phase. The x=0.2 composition sintered at 1100 °C possesses excellent combined microwave properties with εr=11.2, Q×f=71,985 GHz and τf=1.5 ppm/°C. A small amount of B2O3 addition (0.6–1.0 wt%) further reduced the sintering temperature to below 950 °C without greatly deteriorating its microwave dielectric properties. The chemical compatibilities between the composite and Cu or Ag have also been investigated. No chemical reaction was observed between the matrix phase and Cu or Ag. The obtained (1−x) Ba3(PO4)2−xBaWO4 composite ceramics added with small amount of B2O3 (0.6–1.0 wt%) are promising for practical LTCC application.