(1−x)CoTiNb 2 O 8 −xZnNb 2 O 6 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)CoTiNb 2 O 8 −xZnNb 2 O 6 microwave dielectric ceramics, the addition of ZnNb 2 O 6 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 ZnNb 2 O 6 ceramics, the increase of ZnNb 2 O 6 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 0.5CoTiNb 2 O 8 −0.5ZnNb 2 O 6 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/℃.

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