Preparation Of CaFe_0.5Mn_0.5O_3-δ-based Compounds And Study Of Their Wave Absorption Properties

The rapid development of advanced electronic technology over the last few decades has led to serious electromagnetic pollution problems.On the one hand,the normal operation of communication electronics can be interfered with by electromagnetic waves,leading to electromagnetic signal leakage and electromagnetic compatibility problems.On the other hand,prolonged and excessive electromagnetic radiation can pose a threat to human health.Therefore,the increasingly serious electromagnetic microwave pollution puts forward higher requirements for the development of efficient microwave absorbing materials.In this paper,a new Ca Fe_0.5Mn_0.5O_3-δ（CFMO）microwave absorbing material is investigated.Firstly,the preparation process of the material is determined,followed by XRD,SEM,VSM and VNA techniques to investigate the laws of doping and compounding on its microscopic morphology,crystal structure and elemental valence changes on its magnetic and microwave absorbing properties,which are studied as follows:（1）The preparation process of CFMO was first explored.When using the solid phase method for the preparation of CFMO,the samples melted after annealing at 1300℃for 7 days.After annealing at 1000℃and 750℃for 7 days,both did not prepare a pure phase of CFMO;after annealing at 800℃by the sol-gel method,it was in basic agreement with the standard PDF card,but a small amount of stray phases were still present.Finally,after annealing at 750℃by the sol-gel method,the pure phase of CFMO was successfully prepared in complete agreement with the standard PDF card.（2）Sm,Ce element-doped CFMO samples were studied.After the introduction of Sm elements in CFMO,all samples were pure phases and the lattice constants and cell volumes of the samples also had a slight increase with the increase of doping amount.At x=0.15,the size and distribution of the holes are most uniform,which effectively enhances the microwave absorption properties of the samples.The oxygen vacancy content also increases from 12.48%to 18.62%,which enhances the dielectricisation of the material.At a thickness of 3 mm,the best absorption performance is achieved at x=0.15.The maximum reflection loss increases from-11.6 d B to-23.45 d B,the absorption is greatly enhanced,the strongest reflection peak decreases from 11.12 GHz to 8.56 GHz,allowing application at lower frequencies,and the absorption bandwidth increases from0.48 GHz to 3.12 GHz.（3）All samples remained pure after Ce doping,and the lattice constants and cell volumes also increased slightly with the increase of doping.Ce_0.1Ca_0.9Fe_0.5Mn_0.5O_3-δholes are the most uniform in size and distribution,and the increase in oxygen vacancies enhances the dielectricisation capacity.The addition of Ce elements enhanced the dielectric loss capability of the samples and optimised the impedance matching.At a thickness of 3 mm,the strongest reflection loss of the sample reaches-40.47 d B from-11.60 d B and the strongest reflection peak is reduced from 11.12 GHz to 7.92 GHz,allowing better application in the low frequency band,and the absorption bandwidth is increased from 0.48 GHz to 2.72 GHz,with a significant improvement in microwave absorption performance.（4）Finally,the wave absorption properties of CFMO are modified by compounding.The pure phases of CFMO,Co₃O₄ and Fe₃O₄ were prepared by both sol-gel and two-step chemical co-precipitation methods,respectively.CFMO particles were smaller,but CFMO@Co₃O₄ and CFMO@Co₃O₄@Fe₃O₄ were larger in size.The TEM image of CFMO@Co₃O₄@Fe₃O₄ clearly shows that CFMO@Co₃O₄@Fe₃O₄ is divided into three layers and the layers are wrapped.It indicates that the CFMO@Co₃O₄@Fe₃O₄composite was successfully prepared.CFMO@Co₃O₄@Fe₃O₄ has a Hc of 61.4187 Oe,but its Ms,Mr increased to 35.1946 emu g^-1,2.1561 emu g^-1,which is comparable to CFMO and CFMO@Co₃O₄ compared to CFMO,which is very favourable for enhancing the microwave absorption performance.The multiple interfaces from the inner CFMO@Co₃O₄ and the innermost CFMO layer allow for multiple reflections and scattering of electromagnetic waves,increasing the transmission path.A large amount of interfacial polarisation is provided,increasing the dielectric loss.The outermost layer of Fe3O₄ provides effective magnetic loss.The end result is excellent impedance matching with the synergistic effect of magnetic and dielectric losses.At a final thickness of 3 mm,CFMO@Co₃O₄@Fe₃O₄ achieves a reflection loss of-48.79 d B at a frequency of 9.04GHz with an absorption bandwidth of 4.1 GHz.This provides effective absorption of electromagnetic waves in parts of the X-band and most of the Ku-band.