Fabrication And Microwave Absorbing Properties Of BaFe_12-x (Ni (0.5)Cu_0.5Zr)_x/2O₁₉ Ferrite

The microwave absorbing materials have being taken much more attention due to the rapid growing of electronic technique, radar and microwave communication, especially the need of Anti-electromagnetic interference, stealth technology and microwave unreflecting chamber. Ferrites are important microwave absorbing materials because they have both dielectric loss and magnetism loss. Due to its strong anisotropy,large imaginary part of complex permittivity and permeability, the M-type Ba ferrite can meet the need of modern microwave absorbing materials with thin coating,band width,strong absorbing and light weight through element substitution,control pattern of grain and nanometer.In this work, we have successfully synthesized M-type ferrites BaFe_12-x(Ni_0.5Cu_0.5Zr)_x/2 O₁₉ (x=0,1,2,3) and BaFe₉ (Ni_0.5Cu_0.5Zr)_3/2 O₁₉ shell coated on the surface of cenospheres by using sol-gel method. Composites of BaFe ₉ (Ni_0.5Cu_0.5Zr)_3/2 O₁₉/polyaniline were prepared by in-situ polymerization. The phase,crystal structural,microstructure and electromagnetic properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and vector network analyzer. Our main results are summarized as follows:(1) Substituting Ni-Cu-Zr for Fe, M-type ferrites BaFe_12-x(Ni_0.5Cu_0.5Zr)_x/2O₁₉ (x=0,1,2,3) were synthesized by using sol-gel method. The results indicate that: the structures of diffraction peaks of the element substituted samples (x=1, x=2) are consistent with those of the un-doped sample. The peaks shifting to the smaller angle suggests that Ni-Cu-Zr can substitute Fe3+ in BaFe12O19 to form the single phase ferrites. In the XRD diffraction pattern of sample x = 3,there are some weak unknown peaks except the characteristic peaks of BaFe₁₂O₁₉, which indicates that there is 2nd phase for the samples with x 3. The samples with x= 0, 1, and 2 have small reflection rate within the frequency range of 2-18 GHz, but the sample with x = 1 has a resonance peak at 15.8GHz with the maximum reflection rate of - 9.24 dB (thickness of 2 mm).≥(2) Composites of BaFe₉ (Ni_0.5Cu_0.5Zr)_3/2O₁₉/polyaniline were prepared by in-situ polymerization. It is found that composites of BaFe₉ (Ni_0.5Cu_0.5Zr)_{3 /2} O₁₉/polyaniline exhibit good microwave absorbing properties. The composite of BaFe₉ (Ni_0.5Cu_0.5Zr)_3/2O₁₉/PANI ( mass ratio of 1:1, thinness of 2 mm ) has the maximum reflection rate of - 21.7 dB at 11.8 GHz. Keeping the maximal reflecting rate, the resonance frequency can be tuned by changing their thickness.(3) The single phase of BaFe₉(Ni_0.5Cu_0.5Zr)_3/2O₁₉ can be coated on the cenospheres. Compared with the electromagnetic properties of BaFe₉ (Ni_0.5Cu_0.5Zr)_{3 /2} O₁₉, which also prepared by sol-gel method, their dielectric loss tangent and magnetic loss tangent have different frequency dependences. The absorbing properties of BaFe₉ (Ni_0.5Cu_0.5Zr)_3/2 O₁₉ coated on the cenospheres are worse than that of single BaFe₉ (Ni_0.5Cu_0.5Zr)_3/2 O₁₉ at frequency range of lower 11GHz, and are better in higher frequency range. In order to achieve good absorbing property,it is important to choose appropriate cenospheres and control the thickness of coating.