Microwave Dielectric Properties of Columbite-Structure Niobate Ceramics, M²⁺Nb₂O₆

Abstract

The binary niobate ceramics, with the formula MNb₂O₆ where M = a ²⁺ cation, are one of the end members of the perovskite BaM_0.33Nb_0.67O₃ 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 (ε_r) and temperature coefficient of resonant frequency (τ_f) of the TE_01δ 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 ε_r between 17 and 22 and negative τ_f values between –45 and – 76 ppm per °C, and Zn-, Mg-, Ca- and CoNb₂O₆ had high Qxf values of 84 500, 79 600, 49 600 and 41 700 respectively

Keywords: Niobate, columbite, dielectric, microwave, Q (quality factor)