Structure and electromagnetic behavior of BaFe12−2x(Ni0.8Ti0.7)xO19−0.8x in the 2-12 GHz frequency range

The non-stoichiometric Ni2+Ti4+ substituted barium ferrites have been prepared. The structure, complex permeability, complex permittivity and microwave absorption of BaFe12−2x(Ni0.8Ti0.7)xO19−0.8x with 0 ≤ x ≤ 2.0 were measured with X-ray diffraction (XRD), Mössbauer spectroscopy and microwave vector network analyzer. The XRD results show that a single-phase M-type barium hexaferrite can be obtained for x ≤ 1.2. The microwave measurement results show that the non-stoichiometric Ni2+Ti4+ substitution has weak effect on the μ′ and ɛ″, but can significantly affect the μ″, ɛ′ and microwave absorption properties of barium ferrites in the frequency range from 2.0 to 12.0 GHz. With increasing substitution, the peak values of the imaginary part of complex permeability increase first, then decrease slimly, with the maximum of 0.4 for x = 1.2. The variation of absorption loss has been studied as a function of the frequency and the degree of substitution x. The maximum loss reaches −12.6 dB when the substitution amount of the Ni2+Ti4+ ions is 0.8. The peak positions of the maximum loss and imaginary part of complex permeability shift into lower frequency band. The substitution or vacancy content is possibly responsible for this microwave response behavior of the non-stoichiometric Ni2+Ti4+ substituted barium ferrites.