.ba / Cu Doped Of Lamno <sub> 3 </ Sub> Microwave Absorption And The La <sub> 0.8 </ Sub> Of Ba <sub> 0.2 </ Sub> Of Mno <sub> 3 </ Sub> / Ni Composite System Performance Research

The microwave absorbing properties of LaMnO₃ system doped byBa at A site, by Cu atB site, by Ba at A site with by Cu at B site andLa_0.8Ba_0.2MnO₃/Ni were studied systematically. The nano-crystallinepowders of LaMnO₃ doped system were prepared by sol-gel process andthe La_0.8Ba_0.2MnO₃/Ni composite materials were prepared by physicalmixing. The analysis of DSC-TGA and FT-IR at different heat treatmenttemperature for the dry gelatin showed that the formation ofLa_0.8Ba_0.2MnO₃ nano-crystalline experienced four stages which were theevaporation of leaving water, the decomposition of EDTA, thedecomposition of CH3COO^2- and NH₃^- and the formation of perovskite.La_1-xBa_xMnO₃, LaMn_1-yCu_yO₃ and La_1-xBa_xMn_1-yCu_yO₃ were perovskitestructure and their lattice parameters changed when doping contents weredifferent from XRD patterns. The shape of above powders was spherical,the size of them was less than 100nm and the diameter of nickel powderwas about 20nm from SEM. In addition, the resistivity of these sampleswas within semiconductor and changed with the doping contents.The complex permittivity and permeability were measured in thefrequency range of 2～18GHz by microwave network analyzer, thereflection coefficient and the loss tangent were calculated based onmeasured data and the absorption mechanism were studied. The resultsshowed that, the following samples had the best microwave absorbingproperties. The effective width of absorption band above 10dB was2.1GHz and the peak was 25dB when x=0.2 and the thickness was 1.6mmfor La_1-xBa_xMnO₃. The effective width of absorption band was 2.6GHzand the peak was 20dB when y=0.1 and the thickness was 1.6mm forLaMn_1-yCu_yO₃. The effective width of absorption band was 3.1GHz andthe peak was 28dB when y=0.1 and the thickness is 1.8mm forLa_0.8Ba_0.2Mn_1-yCu_yO₃.The effective width of absorption band was 3.4GHzand the peak was 44dB when the mass proportion of La_0.8Ba_0.2MnO₃ was62.5% and the thickness of 1.6mm for La_0.8Ba_0.2MnO₃/Ni.The study of absorption mechanism showed that the dielectric loss of La_1-xBa_xMnO₃ was mainly and the magnetic loss was subordinate. ForLaMn_1-yCu_yO₃ and La_0.8Ba_0.2Mn_1-yCu_yO₃, there was magnetic loss besidesdielectric loss and the two loss factors had opposite change, so the twolosses competed with each other. It was considered that there wereferromagnetic clusters and anti-ferromagnetic clusters in the materialsbecause of doping Cu and the stability of the two clusters could be linkedwith the value of microwave frequency so that they transformed witheach other. The ferromagnetic clusters resulted in magnetic loss andthe anti-ferromagnetic clusters resulted in dielectric loss. The response ofthem to different frequency gave rise to an alternative effect of dielectricloss and magnetic loss. The absorption mechanism of La_0.8Ba_0.2MnO₃/Nisamples was a common effect of dielectric loss from La_0.8Ba_0.2MnO₃ andmagnetic loss from nickel and the space interracial polar relaxation loss.