Preparation And Microwave Absorption Properties Of Doped Barium Ferrite Ceramics

The rapid development of electric information technology pushes applications of electromagnetic wave in civil and military fields,while electromagnetic pollution that endanger human health has been brought simultaneously.Thus,developing microwave absorption materials of large reflection loss and broad bandwidth is becoming meaningful.The inherent properties of microwave absorbing materials,including complex permeability and permittivity,are thought to be significant in enhancing the reflection loss and broadening the effective bandwidth.M-type barium ferrite(BaFe₁₂O₁₉),a versatile material,performs excellent electromagnetic properties due to the large magnetic loss at the natural resonance frequency.Thus,the microwave absorption properties can be adjusted when Fe³⁺ ions are substituted with other trivalent ions or combination of divalent and tetravalent ions.Metal cobalt and nickel are typical magnetic materials.High electron valance Zr⁴⁺ is beneficial to produce multiple resonance peaks.Thus,ionic combinations of Co²⁺-Zr⁴⁺ and Ni²⁺-Zr⁴⁺ may improve the microwave absorption property of barium ferrites.In this work,the solid-state reaction method was used to prepare Ba（CoZr）_xFe_12-2xO₁₉ and Ba（NiZr）_xFe_12-2xO₁₉ written as BMZFO-x（M = Co,Ni）ceramics,x = 0.2,0.4,0.6.The phase composite and surface morphology were studied.Magnetic properties were investigated using a vibrating sample magnetometer.The saturation magnetization increased while the coercive force decreased with an increase in the content of Co²⁺-Zr⁴⁺ and Ni²⁺-Zr⁴⁺.Paraffin and polyvinyl alcohol were applied to fabricate microwave absorbing samples.The electromagnetic parameters of BMZFO-x ceramics were measured by the air-line method.The evident resonance is observed in the curve of μ′′ with polyvinyl alcohol based absorbing samples and the position of resonance peaks varies as x increases.Reflection loss of BMZFO-x ceramics can be calculated using the transmission theory.The reflection loss of BCZFO-x ceramics mixed with polyvinyl alcohol is –28 d B,while the reflection loss of BNZFO-x ceramics is –60 d B and BNZFO-x samples exhibit a wide bandwidth.Thus,ion doping has an important influence on the microwave absorption property.The reflection loss of BaFe₁₂O₁₉ can be enhanced obviously by combination of divalent and tetravalent ions.While high electron valance doping is benifical for chaging the position of loss peaks and broadening bandwidth.Therefore,Barium ferrites doped by Ti⁴⁺（BFTO-x）were synthesized by sol-gel method.The phase structure,magnetic property and microwave absorption ability have been studied.A vector network analyzer was used to investigated the electromagnetic parameters and analyze the microwave absorption property of BFTO-x ceramics.Double resonance peaks are obtained in the curve of μ′′ due to the high valence Ti⁴⁺ and the resonance peaks move towards the low frequency with the increase in x.Paraffin or polyvinyl alcohol were mixed to fabricate absorbers.Polyvinyl alcohol mixed samples perform an excellent microwave absorption property with the maximum reflection loss of –44.9 d B,and the reflection peak drifts from 18 GHz to 4 GHz as thickness varies.The tunable frequency range varying with thickness of BFTO-0.6 ceramics is large,which covers 81% of the investigated frequency.Therefore,BFTO-x ceramics can be a promising candidate applied in a wide frequency range.