Study On The Preparation Of LaCoO₃ And Its Absorbing Properties

The rapid development of society leads to the increasing dependence of human on electronic products.In the daily use of electronic products,electromagnetic wave pollution is inevitable.Health hazard and information leakage caused by electromagnetic radiation have become a serious problem in modern society.Perovskite oxide（ABO₃）has shown great application prospects in microwave absorption due to the coexistence of ferromagnetic order and magnetoelectric coupling effect.LaCoO₃ is a typical perovskite material.In this paper,LaCoO₃ is modified based on the ideas of ion doping,heterostructure design and dielectric-magnetic material composite to prepare high-performance microwave absorbing materials.Firstly,LaCoO₃ matrix was synthesized by the sol-gel method,and then the oxides La Co_1-xFe_xO₃ and La_1-xDy_xCo O₃were prepared by doping Fe and Dy elements.It was found that the phase structure of LaCoO₃ was not changed by the doping of Fe at B site.Fe³⁺/Co³⁺magnetic exchange and ferromagnetic interaction of La-Fe enhance the saturation magnetization of samples.Fe doping improves the impedance matching ability of LaCoO₃.The minimum RL value of La Co_0.9Fe_0.1O₃ reaches-38.99 d B at 10.08GHz,and the effective absorption bandwidth（EAB）is 4.48 GHz.The doping of Dy element at the A site results in the conversion of LaCoO₃ from R 3c to Pm3m phase.Due to the transformation of La_1-xDy_xCo O₃ crystal form,the grain shape changes from ellipse to cube,and the grain size increases significantly,but still remains at nanometer scale.The transformation of crystal form also leads to the change of lattice constant,the shortening of Co-O-Co bond length,and the strengthening of ion exchange and charge polarization between elements.Dy doping also increases the void volume and specific surface area of La_1-xDy_xCo O₃,which is conducive to the electromagnetic wave entering into the material and optimizes the impedance matching.At the matching thickness of 2 mm,the RL_min of La_0.9Dy_0.1Co O₃reaches-33.05 d B at 16 GHz and the EAB reaches 4.8 GHz.The EAB of La_0.85Dy_0.15Co O₃reaches 8.46 GHz at a matching thickness of 2.7 mm.Secondly,Ti O₂@LaCoO₃ with one dimensional long chain structure was prepared by solvothermal and sol-gel method.Ti O₂ nanowires are multiphase structures with rich heterogeneous interfaces.LaCoO₃ particles were aggregated on the surface of Ti O₂ nanowire to construct a heterogeneous interface between LaCoO₃ and Ti O₂,which enhanced the polarization loss ability.The presence of Ti O₂ attenuates the skin effect of LaCoO₃ and improves the impedance matching characteristics.In addition,the one-dimensional chain structure can prolong the transmission path of electromagnetic wave and enhance the attenuation effect.The composite Ti O₂@LaCoO₃ achieves an RL_min value of-41.71 d B and an EAB of 5.12 GHz at a matched thickness of 2 mm.Finally,LaCoO₃ and Fe₃O₄ composites were prepared by simple mechanical ball milling.As the mass fraction of Fe₃O₄ increases,the saturation magnetization of composite materials LaCoO₃ and Fe₃O₄ gradually increases,while the coercivity gradually decreases.The loss mechanism of LaCoO₃ and Fe₃O₄ composites becomes richer and the impedance matching performance is excellent.The test results show that when the mass fraction of Fe₃O₄ is 50%,the sample has the lowest RL_min value（-44.86 d B）and good effective absorption bandwidth（4.08 GHz）,and the matching thickness is only 2.4 mm.In summary,LaCoO₃ powder prepared by sol-gel method was used to prepare four kinds of absorbent materials with excellent properties through ion doping process and composite process,which has certain guiding significance for the modification of perovskite oxide microwave absorbent materials in the future.