Design And Synthesis Of Microwave Absorbents Based On Different Loss Mechanisms And Their Property Study

On basis of different microwave loss mechanism,that is to say,dielectric-magnetic loss mechanism and dielectric loss mechanism,the corresponding FeCo/ZnO/La_0.7Ba_0.3MnO₃composites,core-shell C/Co submicro-composites and LaOCl/C nanocomposites have been prepared and investigated in the present work.The characteristics of the obtained samples have been performed to examine the composition,microstructure and microwave absorption properties through X-ray diffractometer,scanning electron microscope,Raman spectrometer and vector network analyzer.The results are listed as following:?1?FeCo/ZnO/La_0.7Ba_0.3MnO₃ composites:FeCo/ZnO composites were prepared by the liquid reduction methods for the formation of FeCo polyhedrons followed thermal treatment of Zn?Ac?₂.2H₂O under nitrogen atmosphere;FeCo/ZnO/La_0.7Ba_0.3MnO₃ composites were constructed by homogeneously mixing FeCo/ZnO composites with La_0.7Ba_0.3MnO₃ prepared by hydrothermal method.When the layer thickness was 2 mm,the optimal RL value of the FeCo/ZnO/La_0.7Ba_0.3MnO₃ composites at 11.6 GHz was-34 dB and effective absorption band?RL<-10 dB?reached 4.8 GHz;however,FeCo/ZnO composites exhibit a minimum reflection loss of-19.8 dB at 11.5 GHz,and an effective absorption band?RL<-10 dB?of 3.4GHz.The introduction of La_0.7Ba_0.3MnO₃ evidently enhance the bandwidth and RL values.The oxygen vacancy defects in FeCo/ZnO composites result in the interfacial polarization,dipole polarization and high conductivity,which contributes to enhancement of dielectric loss capacity and realizing excellent impedance matching.When La_0.7Ba_0.3MnO₃ was introduced into FeCo/ZnO composites,the microwave absorption was improved due to its ferromagnetic properties and lattice distortion induced dipole polarization.?2?C/Co core-shell submicrospheres:C/Co composites were successfully prepared by liquid synthesis and following heat treatment process.The heat treatment not only can enhance the crystallinity of the prepared C/Co composite,but also induce their core-shell morphology transformation from a snow-flak shell to a enclosed shell.The results show that C/Co composite exhibit excellent microwave absorption property.Minimum reflection loss?RL?can reach-23 dB at 11 GHz with thickness of 2.5 mm,and effective bandwidth?RL<-10 dB?of 3 GHz.When the layer thickness increases,multiple-absorption peaks occur and the absorption peak shifts to low frequencies.The outstanding microwave absorption properties can be attributed to the better impedance matching,dielectric loss and quarter-wave length interference cancellation.?3?LaOCl/C nanocomposites:the lamellar LaOCl/C nanocomposites with LaOCl nanoparticles embedded in carbon matrix have been synthesized.Compared with dielectric loss of LaOCl nanoparticles,lamellar LaOCl/C nanocomposites appear multi-dielectric resonance peaks due to the increase of carbon content,and show excellent microwave absorption properties in 1-18 GHz range,which are attributed to suitable impedance match and microwave attenuation capacity.The optimal reflection loss?RL?is-32 dB at 18 GHz with a thickness of 1.5 mm,and effective bandwidth with RL below-20 dB is 14.8 GHz covering 3.2-18 GHz at the integrated thickness of 1.5-6 mm,indicating that lamellar LaOCl/C nanocomposites would be promising absorbents in microwave absorption field.