Study On Preparation And Property Of BaTiO₃ And Res Doped BaTiO₃ As Radar Absorbing Materials

As the key of stealthy technology, radar-absorbing material (RAM) has been widely used in both military and civil fields. On one hand, RAM is used in weapons to protect them from being detected by radar; on the other hand, RAM is used to protect people from being hurt by electromagnetic radiation. Barium titanate(BaTiO₃) is a kind of dielectric material with microwave absorption property, including dielectric loss as the major and magnetic loss as the minor. As far as dielectric loss is concerned, its mechanism of action is chiefly contributed to conductivity, relaxing polarization and harmonic oscillation.In this thesis, nano powder of BaTiO₃ was synthesized by sol-gel method, and the technique parameters were optimized and determined as following: precursor concentration 0.5mol/L, glacial-acetic acid dosage 400ml/mol precursor, water area temperature 60℃, gel aging time 4h and calcining temperature 850℃for 2h should be employed best. Then BaTiO₃ with Ln REs 0.2% doped was synthesized by the optimum technique process. And the REs chosen were La, Ce, Nd, Eu, Gd, Dy. Besides, with considerations of the improvement of microwave absorption property which La doping had brought, BaTiO₃ with different amount of La(0.6% and 1.0%)doped were also prepared.Then, the dry gel of BaTiO₃ was analyzed by the means of DSC and FT-IR. And the crystal structure and the surface appearance of BaTiO₃ and BaTiO₃ with REs doped were studied by XRD, FT-IR, Raman spectrum and SEM, and the microwave performance by the network-analyzing equipment. At last, we obtained BaTiO₃ with Nd 0.2% doped with Rmin -60dB at 2～18GHz band, and BaTiO₃ with La 0.6% doped with Rmin -44dB at X band.By comparison of BaTiO₃ with 6 kinds of REs 0.2% doped, it was found that doping of REs caused lattice distortion and then a grew larger, c/a and particle diameter decreased and volume of cristal cell shrinked. Besides, the peak intensity of the electromagnetic property constants of BaTiO₃ decreased and the peaks shifted towards blue rigions. Radar absorption property was also improved. And by comparison, it was concluded that Nd or La doping brought a large effect on the electromagnetic property and the microwave absorption property; the effect of Dy doping was less; that of Ce doping was the least; and that of Eu or Gd doping depended on the target property.By analyzing the structure and property of BaTiO₃ with different amount of La doped, we proposed the migration regularity of La³⁺ in BaTiO₃ crystal on the reasonable premise. Based on the above theory, the effect of different amount of La doping was analyzed. Then it was found that: with the amount of La doped increasing, a decreased, the particle diamater and c/a and the volume of crystal cell increased first and decreased afterwards. The peaks of the electromagnetic property constants shifted towards blue rigions and their intensity decreased. The radar absorption property was also improved. But the effect of La doing turned the opposite after some critical value.