.ce / Fe-doped Lamno <sub> 3 </ Sub> System Of Microwave Absorbing Properties

The microwave absorbing properties of LaMnO3 system doped by Ce at A site or doped by Ce at A site and doped by Fe at B site were studied systematically in this paper.The nanocrystalline powders of La _1-xCe _x MnO₃ and La_0.6Ce_0.4Mn_1-yFe_y O₃ were prepared by sol-gel process.DSC-TGA of dry gelatin and FT-IR of different heat treatment of La₍0.6_Ce_0.4MnO₃ were analyzed.It showed that the formation experienced four stages which were the vaporized of leaving water,the decompound of EDTA, the decompound of CH₃COO^2-and NH₃^-,the formed of perovskite.XRD analyzing showed that all the La_1-xCe_x MnO₃ samples were perovskite,but there was a small amount of CeO₂ impurity phase.SEM analyzing showed that the samples of La_1-xCe_x MnO₃ and La_0.6Ce_0.4Mn_1-yFe_yO₃ powders both appeared to be shot rod.The average size of La_1-xCe_xMnO₃ and La_0.6Ce_0.4Mn_1-yFe_yO₃ is about 80 nm and 100 nm.The room temperature resistivity of samples was measured by cylinder method.The results showed that the resistivity of La_1-xCe_x MnO₃ decreased with the increase of Ce element,and the resistivity of La_0.6Ce_0.4Mn_1-xFe_y O₃ increased with the increase of Fe element,but both of them were within semiconductor.The complex permittivity and permeability were measured in the frequency range of 2-18GHz by microwave network analyer,and the reflection coefficient and the loss tangent were calculated based on measured data.The result showed that there was the best effect of microwave absorption for the sample of x=0.4. When the thickness of the sample is 2.20 mm,the highest absorption peak is 27dB and the effective band width of more than 10dB reached 3.2 GHz.The absorption peak of samples were increased and the effective absorption band was broadened when Fe element was incorporated,and there was the best effect of microwave absorption for the sample of y=0.14.When the thickness of the sample is 2.00 mm and y=0.14,the highest absorption peak is 38dB and the effective band width of more than 10dB reached 4.1GHz.The study of absorption mechanism showed that the microwave absorption of La_1-xCe_x MnO₃ and La_0.6Ce_0.4Mn_1-yFe_y O₃ were resulted in by the joint effect of dielectric loss and magnetic loss,and both of them were just contrary to the change with the changes of microwave frequencies.It was possibly caused by the mutual transformation of ferromagnetic clusters and anti-ferromagnetic clusters.The nano-effect and the changes of resistivity and magnetic properties because of being doped played an important role of the absorbing mechanism of the samples.