Microwave Absorption Property Regulation And Mechanism Of Bismuth Ferroelectric Ceramic

Electromagnetic absorbing materials play an important role in aerospace and communication industries.In addition,with the development of society and the progress of science and technology,human living space is also full of various electromagnetic waves,some electronic equipment and important places will inevitably use electromagnetic absorption materials.Ferroelectric has the potential to become a new generation of electromagnetic absorbing materials because its internal polarization unit can convert the electromagnetic wave absorbed into heat through dielectric loss.However,the high dielectric constant and low permeability of common ferroelectrics make the electromagnetic wave reflect on the surface of materials and reduce the electromagnetic absorption performance.At the same time,the low dielectric loss also limits the improvement of electromagnetic absorption performance.In order to improve the electromagnetic absorption performance of ferroelectrics,based on sol-gel method,this paper proposes a series of feasible control strategies,which are briefly introduced as follows:By doping calcium ion with bismuth ferrite A site,the oxygen vacancy increases,and the concentration of phase boundary defect increases,thus the intensity of absorbing peak is improved.At the same time,the special mechanism of calcium ion doping will make the return loss obviously appear double absorption peak,so as to greatly broaden the absorbing bandwidth and realize the improvement of the absorbing performance of the material.When the calcium ion doping concentration is 0.1,the ceramic sample achieves a peak absorption value of-34.5 d B and an effective bandwidth of 0.963 GHz.Through the co-doping of lanthanum A and lanthanum manganese AB,it is found that the lanthanum doping causes the structural phase transformation of bismuth ferrite,and then inhibits the formation of impurity phase.The spatial structure of bismuth ferrite also changes from R3c to orthogonal C222.Lanthanum doping produces ordered domain structures that alter electron coupling states,induce polarization rotation and strong natural ferromagnetic resonance.With the increase of lanthanum doping concentration,the dielectric loss decreases and the magnetic loss also increases.The electromagnetic parameters were adjusted from mismatching to matching,which improved microwave absorption.In this technique,manganese ion doping at the B site was found to inhibit the above structural phase transition.It is also found that the magnetic properties of the ceramic are greatly enhanced with the doping of manganese ions.As predicted,the absorption peak value of-56.238 d B and the absorption bandwidth of 1.089 GHz are obtained when x=0.2 and y=0.04 due to the enhancement of magnetic loss of Bi_1-xLa_xFe_1-yMn_yO₃ system.Through spatially induced interlayer,BiFeO₃ or BaTiO₃ with high dielectric loss is interlayer based on bismuth titanate.The study found that the larger the number of interlayer,the greater the degree of lattice mismatch,the greater the internal stress,and the more unstable the structure.At the same time,the interfacial polarization of the ceramics with odd and even layers is affected by the different symmetry of the perovskite structure in the middle layer.The results show that the Bi₅Fe Ti₃O₁₅ with four-layer structure has an absorbing peak value of-57.439 d B and an effective absorbing bandwidth of 0.9375 GHz when the thickness of BiFeO₃ is 1.0 mm.When BaTiO₃ is interbedded,Bi₄Ba₂Ti₅O₁₈ with a five-layer structure has a peak absorption value of-26.818 d B at 9.4402 GHz when the thickness is 1.4mm,and the corresponding effective bandwidth QB=0.7736 GHz.Obviously,the performance of barium titanate intercalation is far inferior to that of bismuth titanate intercalation,which may be due to the enhancement of dielectric loss after barium titanate intercalation,but also more inhibition of magnetic loss.At the same time,the excellent absorbing properties of Bi₅Fe Ti₃O₁₅ ceramics also guide a new direction for the development of absorbing materials.