Effects of Nb2O5 Doping on the Microwave Dielectric Properties and Microstructures of Bi2Mo2O9 Ceramics

This study investigated the effects of the addition of Nb₂O₅ and sintering temperature on the properties of Bi₂Mo₂O₉ ceramics. The ceramics were sintered in air at temperatures ranging from 620°C to 680°C. The addition of small amounts of Nb₂O₅ as a dopant significantly affected the crystalline phase and the microwave dielectric properties of the Bi₂Mo₂O₉ ceramics. The secondary phase, γ‐Bi₂MoO₆, was observed when Nb₂O₅ was added. However, unlike the Bi₂Mo₂O₉ ceramic without Nb₂O₅ sintered above 645°C, the ceramics with 3 mol% Nb₂O₅ contained no γ‐Bi₂MoO₆ when sintered at 660°C. The Q × f value and τ_f of the Bi₂Mo₂O₉ ceramics were improved by Nb₂O₅ doping. The Bi₂Mo₂O₉ ceramics doped with 2 mol% Nb₂O₅ exhibited the best microwave dielectric properties, with a permittivity of 36.5, a Q × f value (f = resonant frequency, Q = 1/dielectric loss at f) of 14100 GHz and τ_f of +5.5 ppm/°C after sintering at 620°C.