The Electromagnetic And Microwave Absorption Properties Of Several Qusai One-Dimensional Transition Metal Materials

With the development of information technology,electromagnetic interference has a serious impact on human life and environment.Electromagnetic pollution protection has to be settled urgently.Meanwhile,stealth field of military needs high demand to microwave absorption materials.High efficiency,wide band and lightweight become important targets for practical application.In this paper,we investigated the fabrication,electromagnetic properties and microwave absorption of quasi one dimensional Ni chains,Co chains,Ni-Al₂O₃-ZnO nanwire and nanoneedle-like ZnO.The frequency dependence of electromagnetic paprameters of these materials is studied from aspects of loading concentration,temperature and sample thickness.The high-temperature elelctricmagnetic properties and microwave absorption of Ni chains and ZnO are studied.Furthermore,we research the method of tuning microwave absorption by changing thickness,loading concentration,and tempertature,and also discussed the response mechanism of microwave of different absorbers.(1)We fabricated the Ni chains by a facile wet chemical method.The morphology of nickel chains were tailored by adjusting the amount of PVP during the synthesis process.Both the complex permittivity and permeability of the three-dimensional nets constructed by nickel chains present strong dependences on temperature in the frequency range of8.2-12.4 GHz and temperature range of 323-573 K.The peaks in imaginary component of permittivity and permeability mainly derive from interfacial polarizations and resonances,devoting to dielectric and magnetic loss,respectively.The effect from both dielectric and magnetism contribute to enhancing the microwave absorption.The maximum absorption value of the nickel chain nets is?-50 d B at 8.8 GHz and 373 K with a thickness of 1.8 mm,and the bandwidth less than-10 d B almost covers the whole investigated frequency band.These are encouraging findings,which provide the potential advantages of magnetic transition metal-based materials for microwave absorption application at elevated temperature.(2)We fabricated the Co chains by a facile wet chemical method,and investigated the impact from molar ratios between N₂H₄and Co²⁺on morphology of Co chains.The frequency dependence of complex permittvity and permeability were investigated and the magneticl loss is higher than dielectric loss.Some peaks are observed in imaginary component of permittivity and permeability which mainly derive from interfacial polarizations relaxation and magnetic resonances,devoting to dielectric and magnetic loss,respectively and then contribute to enhancing the microwave absorption.The maximum microwave absorption value of the Co chains reachs-35d B at 17.5 GHz with 70wt%loading concentration,and the microwave absorption can be tuned by changing thickness of samples and loading concentrations.(3)In this work,atomic layer deposition(ALD)was employed to fabricate coaxial multi-interface hollow Ni-Al₂O₃-ZnO nanowires.The morphology,microstructure,and ZnO shell thickness dependent electromagnetic and microwave absorbing properties of these Ni-Al₂O₃-ZnO nanowires were characterized.Excellent microwave absorbing properties with a minimum reflection loss(RL)of approximately–50 d B at 9.44 GHz were found for the Ni-Al₂O₃-100ZnO nanowires,which was 10 times of Ni-Al₂O₃ nanowires.The microwave absorption frequency could be effectively varied by simply adjusting the number of ZnO deposition cycles.The absorption peaks of Ni-Al₂O₃-100ZnO and Ni-Al₂O₃-150ZnO nanowires shifted of 5.5 and 6.8 GHz towards lower frequencies,respectively,occupying one third of the investigated frequency band.The enhanced microwave absorption arose from multiple loss mechanisms caused by the unique coaxial multi-interface structure,such as multi-interfacial polarization relaxation,natural and exchange resonances,as well as multiple internal reflections and scattering.These results demonstrate that the ALD method can be used to realize tailored nanoscale structures,making it a highly promising method for obtaining high-efficiency microwave absorbers.(4)We fabricated nanoneedle-like ZnO(ZnO_n)by a facile combustion synthesis route,demonstrated the original observations on complex permittivity of ZnO_n ranging from 298to 573 K and in X band.Both real and imaginary permittivity(??and??)of the ZnO_ndepend on temperature and frequency.The??increases while the??possesses a maximum value with increasing temperature.The maximum value of??appears at 473 K,the corresponding loss tangent increases by 100%than that at 298 K.The relaxations presenting in??mainly arise from the dipole polarization and interfacial polarization in ZnO_n.Multi-region microwave absorption of the ZnO_n appears in the investigated temperature and frequency,as well as thickness.The minimum reflection loss value reaches-44 d B,which is superior to the previous reports.