Characterization and microwave dielectric properties of M2+Nb2O6 ceramics

This paper details the investigation of the quality factor (Q), dielectric permittivity (epsilon(r)) and temperature coefficient of resonant frequency (tau(f)) of the TE01 delta 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 degrees to 1400 degrees C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M = Mn2+, Co2+, Ni2+, Cu2+, and Zn2+ and the group 11 metal cations M = Mg2+, Ca2+, Sr2+, and Ba2+. All columbite niobates were found to have E, between 17 and 22 and negative tau(f) values between -45 and -76 ppm/degrees C, and ZnNb2O6, MgNb2O6, CaNb2O6, and CoNb2O6 had high Qf values of 84 500, 79 6009 49 600, and 41700 GHz, respectively. The Qf of MgNb2O6 was found to rise to over 95 000 GHz when heated at 1300 degrees C for 50 h.