Temperature compensated niobate microwave ceramics with the columbite structure, M(2)(2+Nb)(O)6

Of the niobate ceramics with the formula M2+Nb2O6, several compounds (M2+ = Zn, Mg, Ca and Co) have Qf values (at f = 1-10 GHz) between 40000 and 90000 GHz, offering potential in dielectric resonator applications. However, their temperature coefficient of resonant frequency (tau(f)) values are too high for commercial development, at between -50 and -90 ppm. This paper details the doping of these materials with dielectric ceramics having a large positive tau(f), in an attempt to reduce the overall tau(f) to zero, whilst maintaining a high quality factor (Q). It was also found that doping increased the relative permitivity (epsilon(r)) of the niobates. Several materials have been made with near-zero tau(f), such as 90% CoNb2O6/10% CaTiO3 (tau(f) = +2.0 ppm, epsilon(r) = 25.2 and Qf = 21700 GHz), and 94% CoNb2O6/6% TiO2 (tau(f) = +4.4 ppm, epsilon(r) = 29.6 and Qf = 20 300 GHz). (C) 2003 Elsevier Ltd. All rights reserved.