Tailoring and Fabricating Temperature-Stable ZnNb₂O₆-Ca_0.5Sr_0.5TiO₃ Composite Ceramics for Next-Generation Microwave...

ZnNb₂O₆-based microwave dielectric ceramics have attracted considerable attention due to their high quality factor (Q × f) and low sintering temperature, but their application was limited by poor temperature stability with a large negative temperature coefficient of resonant frequency (τ_f). Herein, novel (1 - x)ZnNb₂O_6-xCa_0.5Sr_0.5TiO₃ (x = 0.05-0.125) composite ceramics were designed and fabricated. The used ZnNb₂O₆ and Ca_0.5Sr_0.5TiO₃ were synthesized through solid-phase reaction by using stoichiometric metal oxides or carbonates as the raw materials at 650 and 1100 °C, respectively. The composite ceramics were prepared by solid-state sintering, and the sintering parameters were optimized at 1175 °C for 4 h by visual high-temperature deformation analysis. A focus was paid on the temperature stability and compositional effects of Ca_0.5Sr_0.5TiO₃ of the obtained composited ceramics. As the Ca_0.5Sr_0.5TiO₃ content increases, the dielectric constant (ε_r) and Q × f gradually decrease, while τ_f shifts toward positive values. At x = 0.075, the composite ceramics sintered at 1175 °C for 4 h exhibit near-zero τ_f (-8.99 ppm/°C), coupled with ε_r = 23.23 and Q × f = 21,686 GHz. This study provides theoretical guide and material support for designing and fabricating various high-performance thermally stable microwave dielectric ceramics for 5G communication devices and future communication technologies.