Investigation Of Preparation And Absorbing Properties Of Rare Earth Elements Doped BaTiO₃ And BaFe₁₂O₁₉

The high speeds of the modern electronics industry development make the electromagnetic Radiation pollute problem increasingly outstanding. Electromagnetic Radiation Pollution has become to be the fourthly pollution following the atmospheric pollution, water pollution and noise pollution and imperil the health of human beings serious. Using absorbing composites would be one of the effective methods to overcome the ectromagnetic Radiation Pollution problem. Therefore it would have great significance to study the absorbing materials. The design and preparation of materials with excellent absorption properties are hot research topics.Barium titanate is a typical electric loss material, and Barium ferrite is a typical magnetic loss materials. The bandwidths of the barium titanate and Barium ferrite are too small for using as microwave absorption materials. The values of the reflection loss are no more satisfactory. It would be instructive to suggest that the rare earth (RE) doped materials have better absorption properties, because the RE elements exhibit not only excellent magnetic properties but also interesting electrical or optical properties. In this paper, the novel RE-doped barium titanate and ferrite particles were investigated. Crystalline structural, microwave absorption properties and their relationships were studied.Nano-particles of BaTiO₃ were prepared by sol-gel process using Ba(CH3COOH)2 and Ti(OC4H9)4 as the starting materials. The optimal technical conditions for BaTiO₃ prepared process were obtained, namely, sol concentration 0.5mol/L precursor, acetic acid dosage 400ml/mol precursor, water bath temperature 60℃and calcining temperature 850℃. The crystal structure, the surface appearance, decompounding process and microwave absorption properties of the sample were studied by means of XRD, Raman, FT-IR, SEM, TG-DTA and network-analyzing equipment. The results show that: the powder obtained is pure tetragonal BaTiO₃, the particle diameter is about 63nm, the bandwidth for attenuation of -10 dB or less is 1.9GHz, the minimum reflection loss is -25dB and appears in 4.4GHz. BaTiO₃ powder exhibits good absorbing properties. The La, Ce, Nd, Eu, Gd and Dy doped BaTiO₃ nanopowders were synthesized by optimal sol-gel method. The influence of REs doping on crystal structure, lattice constant, particle size, surface appearance and microwave absorbing materials were analyzed. The results show that the REs doped samples have the same crystalline tetragonal structure, and the particle sizes are betweent 30nm and 60nm. The particle size of the materials was decreased, lattice constant a enlarged and c decreased.ε',ε",μ′andμ″were shifted toward higher frequency for Re-doped samples compared with undoped sample The reflections of Re-doped samples were decreased. The bandwidths were widen. The doping of RE ions can greatly improve the microwave absorption properties of the BaTiO₃ materials. Effects of Nd, La and Ce doping on reflection are larger, and minimum reflections of three samples are all less than -50dB. Nd and Eu doping gives the greatest contribution to bandwidth and the bandwidths are widen two times. Ce doping contributes least on bandwidth, and the bandwidth is only 0.5GHz. The shift toward higher frequency for La doped samples is most. A Case Study of La, the influences of the La content on structure and properties of barium titanate are investigated. With the increase of La content, the lattice constant a was decreased, particle size and c/a first increased and then decreased. Compared with BaTiO₃, the reflections were decreased and the bandwidths were widening for samples at the La content of 0.2 % and 0.6%.M-type barium ferrite was prepared by sol–gel auto combustion method. The effects of the citric acid and pH on magnetic properties were analyzed. The results show that the adding amount of citric acid had no significant effect on saturation magnetization of BaFe₁₂O₁₉. With the increasing of citric acid, the coercivity of BaFe₁₂O₁₉ was increased. With the increasing of pH, the saturation magnetization first increased and then decreased, the maximum appear in pH = 7.00. With the increasing of citric acid, there were no significant variations on coercivity. According to agglomeration mechanism, the contributivenesses of citric acid, pH and polyethylene glycol on agglomeration control were studied. According to the results, the optimal technical conditions were obtain,namely, olar ratio 2:1, pH 7.0 and polyethylene glycol 20g/L. the calcined temperature of barium ferrite was 850℃for 3h by means of TG-DTA and XRD. The prepared barium ferrite was hexaferrite. The minimum reflectivity was -12dB. The bandwith (<-10dB) was 0.6GHz. the microwave absorbing properties of prepared barium ferrite is poorCe and Dy doped barium ferrite materials were synthesized by optima sol–gel auto combustion method. The effects of RE doping on structure, magnetic and microwave absorbing properties were investigated. The results show that all samples have the same crystalline hexaferrite structure. With the increasing of the REs content, saturation magnetizations of all RE doped samples were almost contant. The saturation magnetizations of all RE doped samples were lower than undoped ones. With the increasing of the REs content, the coercivity of RE doped samples first increased and then decreased, the coercivity was smallest at RE content of 0.2%. At 2¹8GHz, the reflectivity of RE doped samples was smaller than undoped ones. The banwidths of RE doped samples were widening. Ce doping had much more effect on microwave absorption properties than Dy doping.In conclusion, the doping of RE ions can greatly improve the microwave absorption properties of the BaTiO₃ and BaFe₁₂O₁₉ materials.