镧掺杂W型钡铁氧体的微波吸收性能研究

【作者】 刘利强；

【导师】 周克省；

【作者基本信息】 中南大学 ， 凝聚态物理， 2008， 硕士

【摘要】 本文较系统地研究了掺杂稀土元素镧（La）的磁铅石W型铁氧体Ba_1-xLa_xCo₂Fe₁₆O₂₇（x=0,0.1,0.2,0.3）体系的微波吸收特性。用溶胶-凝胶法制备了Ba_1-xLa_xCo₂Fe₁₆O₂₇（x=0,0.1,0.2,0.3）超微粉体。对Ba_0.8La_0.2Co₂Fe₁₆O₂₇样品干凝胶的DSC-TGA和不同热处理温度下的FT-IR分析表明Ba_0.8La_0.2Co₂Fe₁₆O₂₇纳米晶的形成过程分为干凝胶中残留的自由水分子释放和柠檬酸凝胶的熔融、柠檬酸盐的热分解、W型铁氧体晶型的形成三个阶段。XRD分析表明Ba_1-xLa_xCo₂Fe₁₆O₂₇（x=0,0.1,0.2,0.3）样品在1200℃的温度下煅烧2个小时能形成较单一的W型钡铁氧体结构。SEM分析表明Ba_1-xLa_xCo₂Fe₁₆O₂₇样品粉晶均呈块体形状,晶型完整且粒子平均粒径在0.5um以下,小于传统固相法制备的1um以上。测量了所有样品的室温电阻率,均处于半导体范围,但掺杂量对电阻率值有一定的影响。用微波网络矢量分析仪测量了样品的复介电常数和复磁导率,分析了它们的微波电磁频谱,计算了材料的微波反射率和损耗角正切,讨论了样品的微波损耗机制。结果表明:稀土La掺杂量x对Ba_1-xLa_xCo₂Fe₁₆O₂₇样品的吸波性能有很大的影响;当x=0.2时,样品Ba_1-xLa_xCo₂Fe₁₆O₂₇微波吸收效果最好,当样品厚度为1.90 mm时,吸收峰值为16.2dB,10dB以上频带宽度达4.0 GHz。对材料的微波损耗机制分析表明,BaCo₂Fe₁₆O₂₇在掺杂稀土La后出现了电阻率和磁性能的改变,影响了样品的损耗因子。Ba_1-xLa_xCo₂Fe₁₆O₂₇的微波吸收峰所在频率介于介电损耗角正切最大值与磁损耗角正切最大值对应的频率之间,但紧靠近磁损耗角正切最大值对应的频率位置,损耗吸收均来自磁损耗和介电损耗的共同作用,但磁损耗是主要损耗。另外材料的细化也是微波损耗增大的重要原因。更多还原

【Abstract】 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.更多还原