Microwave dielectric properties of columbite-structure niobate ceramics, M2+Nb2O6

The binary niobate ceramics, with the formula MNb2O6 where M = a2+ cation, are one of the end members of the perovskite BaM0.33Nb0.67O3 group (the other being BaO), and often have a columbite structure. Many of the parent perovskite compounds are known to have interesting dielectric properties at microwave (1 - 10 GHz) frequencies, and as such are candidate materials for use in dielectric resonator applications for mobile and satellite communications. A wide range of the columbite niobate ceramics was studied to assess their potential. This paper details the investigation of the quality factor (Q), dielectric permittivity (ετ) and temperature coefficient of resonant frequency (τf of the TE01δ mode of the columbite ceramics. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800 to 1400°C. A comprehensive study was made of the niobates containing the metal cations M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+, as these ions are all of a similar size to the Nb5+ ion, and the group II metal compounds M = Mg2+, Ca2+, Sr2+ and Ba2+ were also studied. All columbite niobates were found to have ετ between 17 and 22 and negative τf values between-45 and -76 ppm/°C, and Zn-, Mg-, Ca- and CoNb2O6 had high Q × f values of 84 500, 79 600, 49 600 and 41 700 respectively.