Temperature compensated niobate microwave ceramics with the columbite structure, M2+Nb2O6

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 40 000 and 90 000 GHz, offering potential in dielectric resonator applications. However, their temperature coefficient of resonant frequency (τf) 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 τf, in an attempt to reduce the overall τf to zero, whilst maintaining a high quality factor (Q). It was also found that doping increased the relative permitivity (εr) of the niobates. Several materials have been made with near-zero τf, such as 90% CoNb2O6/10% CaTiO3 (τf=+2.0 ppm, εr=25.2 and Qf=21 700 GHz), and 94% CoNb2O6/6% TiO2 (τf=+4.4 ppm, εr=29.6 and Qf=20 300 GHz)