Preparation And Electromagnetic Properties Of Zn²⁺ And La³⁺ Substituted Barium W-type Hexaferrite

Ferrite is a very important class of rada absorption material （RAM） because of highabsorptivity, well impedance matching, wide bandwidth and inexpensiveness. But thesecapabilities lie on a thick coating and the RAM has a low absorption at S wave band（2⁴GHz）. To obtain good quality ferrite absorber, we selected the W-type hexagonalbarium ferrite (BaNi₂Fe₁₆O₂₇) for the study and a series of research works have beendeveloped in the thesis, such as molecular formula, preparation and the impact ofelectromagnctic parameters and absorbing properties using different type doping anddifferent amount of doping. The main contents and conclusion can be summarized asfollowing:In the first chapter, we introduce the situation of research about the ferrite absorbingmaterials and the main categories of the ferrite absorbing materials, simply introduce theW-type ferrite and the background and significance of this project.In the second chapter, we introduce some commonly preparation of the W-typebarium ferrite and the characterization of the structure of the samples. Specially, we chosethe sol-gel to prepare samples. We measure the structure of the samples with X-raydiffraction and analysis the phase of it. The results show that the optimum conditions ofpreparation a complete W-type barium ferrite: the proportion of iron and barium isbetween15.7and15.1, we choose15.4in this experiment. The samples are first kept inthe450degrees and heated3hours for pretreatment, then high-temperature sintered for3hours on1280degrees.In the third chapter, we describe the affection in the magnetic properties of W-typebarium ferrite when changing the content of Fe in it or doping Zn²⁺and La³⁺on it. Theresults show that: the content of Fe element has a significant impact in the structure of theW-type barium ferrite, and the absent of Fe can help constitute the structure of W-typebarium ferrite; with the increasing of Zn²⁺doped in the samples the saturationmagnetization increased, the coercive force reduced, which can be explained by thenon-magnetic of Zn²⁺ions; with the increasing of La³⁺doped in the samples the saturationmagnetization and the coercive force were no significant changed, which indicating thatthe doping of rare earth elements cannot significantly improve the W-type barium ferritemagnetic properties. And, the results also show that the maximum doping of La³⁺is y=0.20under our experiment condition through the X-ray diffraction. In the fourth chapter, we describe the measure method of absorbing properties of thesample, and mainly studied the affection of the absorbing properties when changed theamount of Fe in the W-type barium ferrite or doped Zn²⁺and La³⁺ions. The results showthat: The ferrite has the maximum loss when the content of Fe is n=15.4, the bestabsorbing performance when the matching thickness is d=3mm. The doping of Zn²⁺caneffectively improve the W-type barium ferrite dielectric loss and the capacity of magneticloss, and the doping of La³⁺can aslo effectively improve the ability of dielectric loss ofthe W-type barium ferrite, while the ability of magnetic loss was not significantlyimproved. The doping of Zn²⁺and La³⁺can significantly improve the microwaveabsorpting performance of W-type barium ferrite, and by changing the amount of Zn²⁺andLa³⁺can also change the absorption band.