Of Lanthanum-doped W-type Barium Ferrite Microwave Absorption Properties

The microwave absorbing properties of W-type ferrite doped by La were studied systematically in this paper.The ultrafine powders of Ba_1-xLa_xCo₂Fe₁₆O₂₇were prepared by sol-gel process.DSC-TGA analyzing of dry gelatin and FT-IR analyzing of different heat treatment of Ba_0.8La_0.2Co₂Fe₁₆O₂₇showed that the formation of Ba_0.8La_0.2Co₂Fe₁₆O₂₇ crystalline experience can divided into three stages which were the vaporized of leaving water and the melting of citric acid,the thermal decomposition citrate,the formed of perovskite.XRD analyzing showed that all the Ba_1-xLa_xCo₂Fe₁₆O₂₇samples after calcinations at1200℃for 2 hours is nearly single W phase.SEM analyzing showed that the shape of above ultrafine powders particle is hexagonal and the particle average size of samples is below 0.5um which smaller than the size of samples made by traditional solid-state process.In addition,the resistivities of these samples are within semiconductor and change with the La doping cotents.The complex permittivity and permeability were measured in the frequency range of 2-18GHz by microwave network analyer,the reflection coefficient and the loss tangent were calculated based on measured data,the microwave spectrum and the absorption mechanism were studied.The results showed that the La doping contents plays an important role in the effect of microwave absorption.The effect of microwave absorption among the samples is the best when La doping contents is x=0.2.When the thickness of the sample is 1.90mm,the highest absorption peak is 16.2dB and the effective band width of more than 10dB reaches 4.0 GHz.The study of absorption mechanism showed that the resistivity and the magnetic properties of Ba_1-xLa_xCo₂Fe₁₆O₂₇system changes when it is doped La.All the frequencies of absorption peak are between the frequency of maximums of dielectric loss tangent and the frequency of maximums of magnetic loss tangent.Both dielectric loss and magnetic loss result in the microwave absorption,but magnetic loss plays dominant role.In addition,the smallish size plays an important role in the absorbing mechanism of the samples.