Characterization and microwave dielectric properties of M 2+Nb2O6 ceramics

This paper details the investigation of the quality factor (Q), dielectric permittivity (εr) and temperature coefficient of resonant frequency (τf) of the TE01δ mode of the columbite binary niobate ceramics, with the formula MNb2O6 where M = 2+ cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800° to 1400°C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M = Mn 2+, Co2+, Ni2+, Cu2+, and Zn 2+, and the group II metal cations M = Mg2+, Ca 2+, Sr2+, and Ba2+. All columbite niobates were found to have εr between 17 and 22 and negative τf values between -45 and -76 ppm/°C, and ZnNb 2O6, MgNb2O6, CaNb2O 6, and CoNb2O6 had high Qf values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Qf of MgNb2O 6 was found to rise to over 95 000 GHz when heated at 1300°C for 50 h. © 2005 The American Ceramic Society.