Study On The Structure And Absorbing Properties Of M-type Barium Ferrite

As human race enters the electronic information age,electromagnetic radiation has become a potential threat in daily life,and it is extremely urgent to develop new and efficient absorbing materials.Ferrite absorbing materials with strong loss-ability,widely bandwidth and low price have attracted wide attention in recent years.In this paper,samples were prepared using sol-gel method and characterized by a variety of instruments.The effects of element doping on the phase formation,microstructure,grain morphology,elemental valence changes,magnetic properties,microwave absorption properties and other aspects of barium ferrites were explored.Firstly,BaFe₁₂O₁₉（BFO）and its doped oxides Bi_xBa_1-xFe₁₂O₁₉（Bi-BFO）,Ce_xBa_1-xFe₁₂O₁₉（Ce-BFO）,Sr_xBa_1-xFe₁₂O₁₉（Sr-BFO）was prepared by sol-gel method.The samples are all single phase without the formation of the second phase,and the spatial group structure is P63/mcc.Through XRD data refinement,it is found that the lattice parameters of each sample have changed which mine the doped elements have entered the corresponding point of barium ferrite.The morphology of the samples is similar as hexagonal diamond-shaped.The morphology of BFO is relatively loose,while the other doped oxides are more agglomerated.The grain size of BFO varies after doping,but the size is all about 2-4μm.With the increase of doping element content,the agglomeration phenomenon between grains is more obvious,and the ion exchange and charge polarization between elements are strengthened.The valence states of each element in the sample were characterized by XPS.It is found that Fe³⁺will converte to Fe²⁺,which increases the overall magnetic moment of the sample and improves the magnetic properties and microwave absorption properties of the material.Doping also causes the increase of oxygen vacancy content,which is conducive to electromagnetic wave entering the material and enhancing the loss capacity of the material.Because Bi element is a non-magnetic element,the saturation magnetization and coercivity of the sample decrease after doping.Ce and Sr can reduce the sample grain size,lead to grain refinement,enhance the interface polarization,and increase the coercivity.All these three elements can optimize the electromagnetic parameters and impedance matching of the material.The doping increases theε’andε’’of the sample,which improves the dielectric loss capacity of the sample.But forμ’andμ",the effect is not significant,and the values are close to 1 and 0,respectively.The Cole-Cole circle,eddy current loss coefficient,attenuation constant,tangent curve of electric and magnetic loss angle of the samples were drawn It is found that the sample has many kinds of electric and magnetic loss mechanism,and the main loss form is electric loss.Higher attenuation constant corresponds to better microwave absorption capacity.By comparison,the attenuation constant of each doped sample is higher than that of BFO,and the absorption capacity of the samples are also greatly improved compared with BFO.With the increase of Bi content,the reflection loss peak of Bi-BFO shifts to low frequency,from 16 GH to 9 GHz.The 2.4 mm thick sample has a maximum reflection loss of-43.6 d B at the frequency of 10.1 GHz.When the doping amount is x=0.2,the effective absorption bandwidth of the material reaches 6.3 GHz,which has the best bandwidth performance.The maximum reflection loss of Ce-BFO（x=0.15）is-41.36 d B at 2.4 mm,10.8 GHz.When the doping amount is x=0.1,the effective absorbing bandwidth of the sample with the thickness of 2.4 mm is 4.24 GHz,which can cover the whole Ku band well.For Sr-BFO sample,the reflection loss increases first and then decreases with the increase of sample thickness when the doping amount is x=0.3,and the absorption peak shifts to low frequency.At 13.92 GHz,the maximum reflection loss of 6 mm thick sample is-33.03d B.When x=0.2,the maximum effective absorption bandwidth is 3.5 GHz.By means of doping modification,the effective absorption bandwidth and absorption efficiency of barium ferrite were greatly improved,which broadened the application range and provided a new idea for the preparation of new microwave absorption materials.