Effects of Nb 2 O 5 Doping on the Microwave Dielectric Properties and Microstructures of Bi 2 Mo 2 O 9 Ceramics

This study investigated the effects of the addition of Nb 2 O 5 and sintering temperature on the properties of Bi 2 Mo 2 O 9 ceramics. The ceramics were sintered in air at temperatures ranging from 620°C to 680°C. The addition of small amounts of Nb 2 O 5 as a dopant significantly affected the crystalline phase and the microwave dielectric properties of the Bi 2 Mo 2 O 9 ceramics. The secondary phase, γ‐ Bi 2 MoO 6 , was observed when Nb 2 O 5 was added. However, unlike the Bi 2 Mo 2 O 9 ceramic without Nb 2 O 5 sintered above 645°C, the ceramics with 3 mol% Nb 2 O 5 contained no γ‐ Bi 2 MoO 6 when sintered at 660°C. The Q  ×  f value and τ f of the Bi 2 Mo 2 O 9 ceramics were improved by Nb 2 O 5 doping. The Bi 2 Mo 2 O 9 ceramics doped with 2 mol% Nb 2 O 5 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.