Synthesis, characterization and dielectric properties of a novel temperature stable (1-x)CoTiNb₂O₈-xZnNb₂O₆ ceramic

(1-x)CoTiNb₂O₈-xZnNb₂O₆ microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing the τ_f value and improving the thermal stability. The phase composition and the microstructure were investigated using X-ray diffraction, Raman spectra, and scanning electron microscopy. A set of phase transitions which were induced by composition had been confirmed via the sequence: rutile structure→coexistence of rutile and columbite phase→columbite phase. For (1-x)CoTiNb₂O₈-xZnNb₂O₆ microwave dielectric ceramics, the addition of ZnNb₂O₆ content (x = 0-1) led to the decrease of ε_r from 62.98 to 23.94. As a result of the high Q × ƒ of ZnNb₂O₆ ceramics, the increase of ZnNb₂O₆ content also led to the lower sintering temperatures and the higher Q × ƒ values. The τ_f value was reduced from +108.04 (x = 0) to - 49.31 ppm/℃ (x = 1). Among them, high density 0.5CoTiNb₂O₈-0.5ZnNb₂O₆ ceramics were obtained at 1175 ℃ with excellent microwave dielectric properties of ε_r 39.2, Q × ƒ 40013 GHz, and τ_f + 3.57 ppm/℃.