Structure and microwave dielectric properties of Ba3(VO4)2–Zn2−xSiO4−x ceramic composites

Microwave dielectric ceramic composites with compositions of (1 − y)Ba3(VO4)2–yZn2−xSiO4−x (y = 0.4–0.6, x = 0.13) have been prepared by firing mixtures of Ba3(VO4)2 and Zn1.87SiO3.87. The X-ray diffraction (XRD) analysis revealed that Zn2SiO4 with a willemite phase can be obtained by appropriately controlling the ZnO deficiency. The starting Zn1.87SiO3.87 powder should be thus composed of the ZnSiO4 crystal phase and redundant SiO2 amorphous phase at room temperature. The scanning electron microscopy studies demonstrated the coexistence of Zn2SiO4 and Ba3(VO4)2 phases in the sintered bodies, as further confirmed by the XRD and Raman results. The near-zero temperature coefficients of the resonant frequency (τf) could be achieved by adjusting the relative content of the two phases owing to their opposite τf values. The existence of a slight amount of secondary phases, element interdiffusion and non-stoichiometry such as Zn deficiency altogether made the predicted property values deviate from the experimentally measured ones. The composite ceramics with 40 wt% Zn1.87SiO3.87 sintered at 1100 °C exhibited desirable microwave dielectric properties of the quality factor Q × f ∼ 23,000 GHz, dielectric constant ɛr ∼ 9.3, and τf ∼ 0.4 ppm/°C.