Structure and dielectric properties of Sb ₂O ₃ foped Zn-Nb-O based microwave ceramics

(ZnNb ₂O ₆- Zn ₃Nb ₂O ₈) -Sb ₂O ₃(ZZS) ceramics were fabricated by the conventional ceramic processing. The effects of the contents of Sb ₂O ₃ on the microstructures and dielectric properties of ZZS ceramics were investigated. The results showed that Sb ₂O ₃ accelerated the sintering of ZnNb ₂O ₆ -Zn ₃ Nb ₂O ₈ ceramics. No other phase was observed in the ceramics except the two main phases of ZnNb ₂O ₆ and Zn ₃Nb ₂ O ₈. It was shown that Sb ³⁺ could change into Sb ⁵⁺ and replace Nb ⁵⁺ or Zn ²⁺ to form the substitutional solid solution. The dielectric constant (ε _r) increased firstly and then decreased with the increase of the content of Sb ₂O ₃, but maintained between 23 and 25, while the dielectric loss has increased slightly. At the microwave frequency range, the dielectric constant of 0.7ZnNb ₂O _6-0.3Zn ₃Nb ₂O ₈ decreased slightly and the value of Q×f increased firstly and then decreased with the content of Sb ₂O ₃. The ceramic with the composition of 1% of Sb ₂O ₃ showed the optimal dielectric properties of ε _r=22.88 and Q×f=38 871 GHz.