Controlled Synthesis And Electromagnetic Properties Of Fe-doped MnO₂

Fe-doped MnO2with different morphologies and crystal structures were synthesized via a boiling process and a hydrothermal method. XRD, SEM, and vector network analysis were adopted to characterize structures, morphologies and electromagnetic properties of the obtained samples. Influence of experimental condition on Fe-doped MnO2was investigated. The first-principles was first used to simulate and calculate the structure of MnO2, and the impacting mechanism of Fe doping on microwave electromagnetic properties of MnO2was discussed preliminary at the level of micro electronic states.In boiling conditions, a small amount of Fe-doping led to the formation of a-MnO2hollow microspheres. Properly increase the doping amount could effectively enhance permeability value and magnetic loss of MnO2, but could decrease its dielectric properties. Excessive Fe-doping resulted in the formation of clewlike or irregularly shaped (Feo.67Mno.33) OOH micro/nanoparticles, which exhibited low value of electromagnetic parameters.In hydrothermal conditions, increasing reaction time and temperature conduced to high crystallinity of Fe-doped MnO2. The transformation from a-MnO2into ε-MnO2was achieved via increasing Fe-doping amount, decreasing solution concentration or reducing (NH4)2S2O8dosage. Excessive dosage of (NH4)2S2O8led to a morphologic change from hollow microspheres to uniform nanorods. The uniformity of particle size could be improved by controlling hydrothermal temperature, which could lead to dimension effect. As an absorbing material, Fe-doped MnO2exhibited enhanced dielectric properties with decreasing doping amount and increasing both reaction time and solution concentration. Proper Fe-doping and increasing (NH4)2S2O8dosage could effectively enhance magnetic loss properties of MnO2.The formation of hollow structured MnO2could be illustrated by "Ostwald ripening process". The hollow degree and surface morphology were affected by experimental condition. Fe3+ions increased the ionic strength and the chemical potential, making hollow structures more available. The surface morphology was affected by Fe+via limiting the crystal growth.Fe-doping resulted in crystal distortion, and thus stumbled polarization process, which led to decrease of dielectric properties. Meanwhile, it changed the ratio and distribution of Mn3+and Mn4+, probably led to spin-glass behavior and enhancement of magnetic loss properties, predominantly driven by the spin wave resonance mechanism. The Fe-involved substitutional solid solution may have good magnetism and result in increased magnetic loss. The results of the first-principles calculation corresponded with experimental phenomena. Fe doping enhanced the strength and length and thus the potential energy of metal-O covalent bonds. It reduced the damping force response of electron cloud to external electric field and finally decreased dielectric loss of MnO2. The density of states of spin-up and spin-down electron of MnO2exhibited an obvious unsymmetrical distribution. The spin polarization of electronic states was promoted to transform MnO2from non-magnetic to mangnetic, resulting in an increase of permeability.