Temperature-stable crystal structure and microwave dielectric properties of BaSi₂O₅-Ba₃V₂O₈ composite ceramics

(1-x)BaSi₂O₅-xBa₃V₂O₈ (x = 0.05–0.25 in molar) novel low-dielectric ceramics were successfully synthesized and investigated via a solid-state sintering process. X-ray photoelectron spectroscopy proved that the valence of V element is V⁵⁺ without V⁴⁺ and Ba₃V₂O₈ is a pure phase in the composite ceramics. The coexistence of BaSi₂O₅ and Ba₃V₂O₈, without other phases, was demonstrated by X-ray diffraction and Raman spectroscopy. Furthermore, scanning electron microscopy combined with energy dispersive spectroscopy indicated the composition of grains and the distribution of the two phases. τ_f value close to zero was obtained in the composite ceramics with x = 0.2. Meanwhile, for 0.8BaSi₂O₅–0.2Ba₃V₂O₈ ceramics after sintered at 1140 °C, the fantastic microwave dielectric properties were found: ε_r = 9.34, Q × f = 55,641 GHz, and near-zero τ_f of 0.14 ppm/°C, which make 0.8BaSi₂O₅–0.2Ba₃V₂O₈ a pioneering candidate for 5G microwave applications.