Study On The Preparation Of SrMnO₃ And Its Absorbing Properties

With the development of national economy,the wide application of modern electronic equipment has also produced serious electromagnetic wave pollution.In order to solve this problem,the development of new and efficient absorbing materials has become an urgent need.Because manganese perovskite oxides have both dielectric loss and magnetic loss mechanisms,they have potential application value in the field of electromagnetic wave absorption,thus becoming a research hotspot.In this paper,the structure and morphology of Sr Mn O₃ were regulated by doping and composite modification respectively,and the effects of different modification on the absorbing properties of materials were investigated.The SMO,Nd-SMO,and Gd-SMO were prepared by the sol-gel method and the sol-gel pressing and sintering method are all of Sr Mn O₃ structure.The XRD results showed that ion doping has led to partial transformation of hexagonal Sr Mn O₃ into cubic Sr Mn O₃.Combining the results of refining XRD image with GSAS software,it can be seen that the space group gradually changes from p63-mmc to pm-3m,and the two-phase unit cell parameters（a、b、c）and unit cell volume（V）gradually increase.The morphologies of the prepared SMO and Nd-SMO samples are agglomerated.With the increase of Nd³⁺doping content,the particle size of the sample gradually decreased,the specific surface area expanded,and the porosity increased.On the contrary,the Gd-SMO sample had a denser morphology and a larger particle size due to the sintering process of the pressed ceramic sheet.It was found by XPS characterization that Mn⁴⁺in the doped lattice was transformed into Mn³⁺,which was beneficial to the occurrence of Mn⁴⁺-O-Mn³⁺superexchange interaction and enhanced the internal conductive loss of the material.Due to the magnetic properties of rare earth elements（Nd,Gd）,the saturation magnetization of Nd-SMO and Gd-SMO samples was improved by Nd³⁺and Gd³⁺doping.We modified the samples based on Nd-SMO and Gd-SMO,and prepared lighter absorbing materials Nd-SMO/Si O₂ and Gd-SMO/Si O₂ by chemical method.Because the prepared Si O₂ is amorphous,the main diffraction peaks in the XRD diffraction spectra of Nd-SMO/Si O₂ and Gd-SMO/Si O₂ are still the characteristic peaks of Sr Mn O₃,and the characteristic peaks of Si O₂ are not obvious.It can be found by SEM that the prepared Si O₂microspheres were randomly dispersed on the surface of the sample,the size of the microspheres was uniform,and the radius size was less than 1μm.Ion doping increased the complex permittivity and complex permeability of the material,which means that the material’s ability to store and consume electromagnetic waves was enhanced.Sr_0.85Nd_0.15Mn O₃ has the lowest reflection loss-33.4 d B when the thickness is 2.4mm,f=7.84 GHz,and the effective absorption bandwidth is 1.76 GHz.When the sample thickness is 5 mm,the reflection loss of the sample at 2.96 GHz is less than-10d B,fully realizing the effective absorption in the low frequency band.When the thickness of Sr_0.94Gd_0.06Mn O₃is 2.2 mm,the reflection loss reaches-36.6 d B at f=9.84 GHz.Si O₂microspheres are combined with Nd-SMO and Gd-SMO to adjust the dielectric loss of the material to improve the impedance matching effect of the material and enhance the absorption capacity of the material to electromagnetic waves.The composite material Nd-SMO/Si O₂-1 achieved the lowest reflection loss-29.2 d B at 2 mm,f=13.04 GHz,and the composite material Nd-SMO/Si O₂-2 achieved the maximum effective absorption bandwidth of 4 GHz at a thickness of 2.00 mm.In addition,the composite material Gd-SMO/Si O₂-2has the best reflection loss of-43.5 d B at f=13.6 GHz,and the maximum effective absorption bandwidth of 3.76 GHz,and the matching thickness is only 2 mm.This confirms that ion doping and compounding are feasible modification methods for manganese perovskite,which is conducive to the improvement of microwave absorption performance of materials.