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.
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