Effects of Postdensification Annealing on Microwave Dielectric Properties of Ba([Mg 1− x Co x ] 1/3 Nb 2/3 )O 3 Ceramics

Effects of postdensification annealing on microwave dielectric properties of Ba([ M g 1− x C o x ] 1/3 Nb 2/3 )O 3 ceramics have been investigated. The 1:2 ordered complex perovskite structure is obtained in the entire composition range of the as‐sintered samples, and the ordering degree decreases with increasing x . With increasing x , the dielectric constant (ε r ) increases, the temperature coefficient of resonant frequency (τ f ) shifts toward negative and can be tuned to near‐zero for x  =   0.6, while the Q ×  f value decreases. With postdensification annealing at 1400°C in air for 24 h, the ordering degree increases, and Q ×  f value can be significantly improved without obvious change in ε r , while the composition for obtaining near‐zero τ f shifts to x  =   0.8. Annealing at 1375°C and 1425°C in air for 24 h does not improve microwave dielectric properties more than annealing at 1400°C. A good combination of microwave dielectric properties of Ba([Mg 1− x Co x ] 1/3 Nb 2/3 )O 3 ceramics after postdensification annealing at 1400°C in air for 24 h has been obtained for x  =   0.8: ε r  = 31.7, Q ×  f  =   76,900 GHz, τ f  = 3.3 ppm/°C.