Preparation And Properties Of Dual-ion Co-doped Barium Ferrite Millimeter Absorbing Materials

As we enter the era of the information revolution,the development of global information technology has made people’s lives more and more convenient.But it also brings a lot of negative effects.The application range of 5G technology is 450MHz-6.0GHz and 24.25-52.6 GHz.The frequency band used by radar is usually an air window with low transmission loss in air.Specially,the frequency band used by fire control radar is 35GHz.So high-performance millimeter wave absorbing materials are in urgent need of research and development.Barium ferrite has a huge magnetic loss because of its natural resonance,so it is a potential wave-absorbing material.However,barium ferrite does not have a natural resonance peak at 35 GHz in the air window,and its single resonance peak cannot form an obvious magnetic loss,which limits its application as a millimeter-wave absorbing material.In this thesis,V⁵⁺-Ni²⁺co-doped barium ferrite powders BaFe_12-xV_xNi_xO₁₉ was prepared.Co-doping Ni²⁺with a radius larger than Fe³⁺will cause lattice expansion of barium ferrite to offset lattice contraction caused by only doping V⁵⁺.And it will solve the problem that the doping amount cannot be increased when doping the V⁵⁺alone.Compared with the vanadium-doped barium ferrite,V⁵⁺-Ni²⁺co-doped can reduce the natural resonance frequency of barium ferrite to 31GHz and get broader bandwidth.When the doping concentration x is equal to 0.6 and the matching thickness is 2mm,the RL of V⁵⁺-Ni²⁺co-doped barium ferrite can reach<-60dB,and the absorption bandwidth can reach 8GHz.And by adjusting the doping ion concentration,different barium ferrites can all show absorbing effect in the range of 30⁴0GHz.This thesis also prepared the vanadium-zinc co-doped barium ferrite BaFe_12-xV_xZn_xO₁₉ by sol-gel method,which solved the problem of easily forming volatile Ni（CO）₄ during the preparation of V⁵⁺-Ni²⁺co-doped barium ferrite.Moreover,Zn²⁺is a non-magnetic ion which can reduce the magnetic crystal anisotropy field of barium ferrite better than Ni²⁺.The effect of V⁵⁺-Zn²⁺co-doped barium ferrite doping amount on the phase structure,morphology,hysteresis loop,electromagnetic properties and microwave absorption properties of barium ferrite was studied.It was found that co-doping of vanadium and zinc can reduce barium ferrite magnetic crystal anisotropy field and generate multiple Landéfactors.When the doping concentration x is equal to0.6,the natural resonance peak can be shifted to around 28GHz and when the matching thickness of vanadium-zinc co-doped barium ferrite is 3.3mm,the reflection loss can be lower than-68.3dB and the absorption bandwidth can reach 8GHz.When the matching thickness is 3.04mm,the absorption bandwidth can reach 10.7GHz,which confirm that vanadium-zinc co-doped barium ferrite is a good absorbing material suitable for millimeter waves.