La_1-x（K_x、Ag_x）MnO₃体系的微波吸收特性研究

【作者】 齐伟；

【导师】 周克省； 黄生祥；

【作者基本信息】 中南大学 ， 凝聚态物理， 2011， 硕士

【摘要】 掺杂稀土锰氧化物因其巨磁电阻效应和奇异的电磁特性,多年来一直是磁电子功能材料领域的一个研究热点。因为其特殊的电磁性能,这类材料可能成为一类新型微波吸收材料,但有关报道少见。本文研究了A位分别掺K和Ag的LaMnO3体系的微波吸收特性。用溶胶-凝胶法制备了La1-xKxMnO3和La1-xAgxMnO3纳米粉体,用DSC-TG、EDS、XRD、SEM对样品的形成过程、成分、晶体结构、微观形貌进行了系列表征分析。研究结果表明,样品的形成过程分为吸附水蒸发、EDTA分解、硝酸根离子分解以及钙钛矿晶型的形成等阶段；La1-XKxMnO3和La1-xAgxMnO3纳米粉体晶体结构均为钙钛矿型,且随着掺杂量增加和温度的升高,样品中均有少量杂相出现。两种样品的颗粒形貌均呈不规则椭球状或短棒状,La1-xKxMnO3和La1-xAgxMnO3样品颗粒平均粒径分别约60nm和100nm。用微波网络分析仪测试了La1-xKxMnO3和La1-xAgxMn03在2-18GHz频率范围内的复介电常数和复磁导率,计算了样品在该频率范围的微波反射率和电磁损耗角正切,分析了掺杂量和样品厚度对体系微波吸收性能的影响及微波损耗机制。结果表明,x=0.3时,厚度2.40mm的La1-XKxMnO3在9.9GHz位置处吸收峰值为27.1dB,大于10dB频宽为10.6GHz; x=0.15时,厚度2.60mm的La1-x AgxMnO3在12.0GHz处吸收峰值为24.9dB,大于10dB频宽为7.1GHzoLa1-xKxMnO3和La1-xAgxMnO3样品兼具介电损耗和磁损耗,但介电损耗相对较强。两种损耗角正切随微波频率的变化相反,可能是基体中铁磁与反铁磁团簇在微波电磁场作用下相互转变或竞争引起。更多还原

【Abstract】 Doped rare-earth manganeties have been becoming a hot and active topic in the field of magnet-electron functional materials because of their giant magnetoresistance effect and special electromagnetic properties over the years.Owing to the properties, it’s possible that such materials become a new type of microwave absorbing materials, but few are reported. The microwave absorbing properties of LaMnO3 system doped by K and Ag at A site respectively were studied in this thesis.The nano-crystalline powder samples of La1-xKxMnO3and La1-xAgxMn03 were prepared by sol-gel method.The formation, composition, crystal structure and particle morphology of these samples were characterized by DSC-TGA,EDS,XRD,SEM. The results showed that the formation of the samples were consist of water evaporation EDTA decomposition, nitrate decomposition and perovskite crystalline growth. Both the crystal structure of La1-xKxMnO3nanocrystalline powders and La1-xAgxMn03 were perovskite type, and A small amount of impurity phase appeared in the samples with the increasing of doping components and temperature. Their crystal powder morphology was irregular ellipsoidal shape or short rod, and the average size of La1-xKxMn03 sample particles was about 60nm and La1-xAgxMn03 about 100nm.Their complex permittivity and complex permeability were measured by microwave vector network analyzer in the frequency range from 2 to 18 GHz, and the reflection coefficient and loss tangent were calculated according to measurements. The effects of doping and thickness on microwave absorption of them and the microwav loss mechanism were discussed. The results showed that the absorption peak of Lai-xKxMn03 with 2.20 mm thickness (x= 0.3) was 27.1dB at 9.9GHz and its bandwidth above lOdB was 10.6GHz,and Lai-xAgxMn03 with 2.60 mm thickness (x=0.15) was 24.9dB at 12.0GHz and bandwidth 7.1 GHz.They had both dielectric loss and magnetic loss, but the former is relatively stronger.lt was possibly caused by a mutual transformation or competetion between ferromagnetic and antiferromagnetic clusters of the matrix in the microwave electromagnetic field that magnetic and dielectric loss tangent changed inversely with the changes of microwave frequency.更多还原