Studies On Preparation, Characterization And Absorbing Microwave Properties Of Hexaferrite Doped With Rare Earths

The efficiency of information expressing is increased remarkably due to microwave technology applied widely in radar, navigation, satellite and communication regions. So microwave technology is a technological revolution having great effect on the world. However, microwave technology offered human more convenience along with the electromagnetic wave radiation not be neglected. As a result, microwave material has attracted more attention and become an interesting research region. As one type of microwave absorbing materials, the ferrite has located the important position due to lower cost, high resistivity and high magnetic permeability at microwave frequency range. Hexagonal ferrite, one of ferrites family, applied to use as the absorbing material for electromagnetic wave at high frequency range. The ferrites doped with small amount rare earth ions have better absorbing wave properties, but the systemic research on this work has not been reported so far. In this paper, the W-type ferrite Ba1-xLaxCo2Fe16O27 doped with La, Nd, Sm, Tb, Er and Yb, respectively, were synthesized by solid reaction method and a sol-gel method, and the Z-type ferrite Ba3-xLaxCo2Fe24O41 doped with La, Nd, and Sm were synthesized by a sol-gel method. By using X-ray diffractometry (XRD), Infrared Spectra (IR), Thermal analyses (DTA-TG), Inductively coupling plasma-atom emission spectrometer (ICP-AES), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS), the phase transformation mechanism and conditions of metal ions were analysized, and the effect of synthesized conditions on the structure of material and the effect of different rare earth ions on the magnetic and absorbing wave properties were studied.The synthesized conditions were studied and the optimum conditions were obtained. The conditions of W-type ferrite were as following: the sintered temperature and sintered time by solid reaction method are 1250℃and 3h; the sintered temperature, sintered time, the ratio of metal ions and citric acid, and pH value by a sol-gel method are 1150℃, 3h, 2:3 and 6.0, respectively. For Z-type ferrite prepared by a sol-gel method , the sintered temperature, sintered time, the ratio of metal ions and citric acid and pH value are 1250℃, 5h, 2:3 and 6.0, respectively. Under the above conditions, the maximum amounts of different rare earth ions were selected and the mole fraction of maximum amount is not more than 0.30 for all of rare earth ions.The results of cell parameters show the change tread is corresponding to the tread of saturation magnetization when the rare earth ions amount is increased. By IR, XPS, TG-DTA and chemical titrition analytical method, the following results were obtained. The absorbing vibration spectra of Fe2+-O was found at 500cm-1, and the presence of Fe2+ was proved by chemical titration method, this indicated Fe3+ was deoxidized Fe2+. The valence state of cobalt is divalent by XPS. The results of TG-DTA show the temperature of forming W phase increases with more addition of La3+ amount, which the temperature is 1220℃without La3+, the temperatures are 1217℃, 1227℃and 1238℃when the mole fractions of La3+ are 0.1, 0.2, 0.3, respectively. This phenomenon is produced due to the distort structure. After rare earth ion was doped, the more distort structure took place, which results in the formation temperature increase.The magnetic properties of W-type and Z-type ferrites doped with rare earth ions at room temperature were tested by vibrating sample magnet meter. The results indicated the effects of La, Nd, Sm ions on magnetic properties of W-type and Z-type ferrites and the effects of Tb, Er and Yb ions on magnetic properties of W-type ferrite have the same tread. They made saturation magnetization(σs) decrease with the increase amount of rare earth ions . Coercovier forces (Hc) for ferrites doped with La, Nd and Sm show visalating tread with the increase of rare earth ions, however, Hc for ferrites doped with Tb, Er and Yb ions increase with the increase of rare earth ions.The permittivity and permeability of the ferrites doped with rare earth ions were tested by using network analysis measurement. The results show that the real part (εr′) and the imaginary part (εr″) of the permittivity and the imaginary part (u r″) of the permeability increase with the increase of the rare earth ions amount,however, the real part (u r′) of the permeability decrease with the increase of the rare earth ions amount . With the increase of rare earth ions amount, the position of resonance peak shift towards to the lower frequency. The electromagnetic loss and the simulation curves of reflection of the ferrite prepared were researched. The results show the addition of rare earth increase the electromagnetic loss (tgδ) and tgδincrease with the increase of rare earth ions. The positions of absorbing peak at the simulation curves shift towards to the lower frequency and this change is corresponding to the change of resonance peak for the u r″- f curves.The usable results and laws were obtained by studying systemical W-type and Z-type ferrites doped with rare earth ions. This offered an effective method for improving the absorbing wave properties of ferrite and a new road for the reasonable use of rare earth ions.