The effect of non-stoichiometry on the microstructure and microwave dielectric properties of the columbites A2+Nb2O6

Both the microstructure and microwave dielectric properties of sintered columbites with the composition A2+1+xNb2O6 (A2+ = Mg, Zn, Co) were analysed. The slight changes in the Nb/A ratio in studied systems have been found to noticeably affect the microwave quality factor (Q) of the ceramics. Regardless of the A2+ ion the dependencies of a Q-factor magnitude on chemical composition demonstrate rather a non-linear trend. Very low products Q × f measured for all studied systems at x < 0 can be attributed to the presence of secondary phase Nb2O5. At x ≥ 0 the Q × f magnitude passes through the maxima subject to the A2+ ion. The highest products Q × f ≥ 110,000 GHz have been found in the Mg and Zn-containing columbites at x = 0.03 and 0.01, respectively, whereas in the case of Co-containing analogues the maximum Q × f = 82,000 GHz corresponds to stoichiometric composition.