Determining the Actual Composition of Nb5+–Ni2+ Codoped Barium Ferrites to Controllably Regulate the Microwave Absorbing Properties

The substitution amount of foreign ions for Fe3+ ions significantly influences the electromagnetic and microwave absorption performance of barium ferrite. To establish the correlation between composition and property, Nb5+–Ni2+ codoped M-type barium ferrite powders with molar ratio of the added Ba2+, Fe3+, Nb5+, and Ni2+ ions being 1:(12–2x):x:x (x = 0–0.8) were prepared by the sol–gel method. The actual substitution amount of Nb5+ and Ni2+ ions for Fe3+ ions are theoretically determined based on the measured concentrations of Fe2+ ions, surface absorbed oxygen, and the lattice parameters of the doped barium ferrite. The calculation results demonstrate that the substitution amount of Ni2+ ions is obviously lower than that of Nb5+ ions in the doped barium ferrites, while the total substitution amount of Nb5+–Ni2+ is still higher than the only Nb5+ ions doping case. As a result, the multiresonant permeability is obviously achieved and dual reflection loss peaks with broad bandwidth ∼12 GHz are apparently observed in the BFNNO with x = 0.4–0.6 over 18–40 GHz. Moreover, the frequency of reflection loss peaks can be adjusted to cover wider frequency range −18 GHz to +40 GHz with variation of x from 0 to 0.8. The developed theoretical calculation approach provides powerful guidance for the controllable design of material composition and regulation of microwave absorption.