The Investigation Of Synthesis And Electromagnetic Characteristics Of Flake-shaped Barium Titanate Powder

In this dissertation,the flake-shaped barium titanate(FBT) powders were firstly prepared by a modified sol-gel method using n-butanol and ethanol as solvent respectively, and barium titanate(BT) powders were prepared by the conventional sol-gel method as contrast.The reflection loss(RL) of FBT/epoxide resin(ER) composite with different weight fractions of FBT and BT/ER composite with different weight fractions of BT were investigated.The prepared FBT and BT powders were characterized by differential thermal analysis (DTA),thermogravimetry analysis(TG),X-ray diffraction(XRD),Raman spectra,scanning electronic microscope(SEM),transmission electron microscope(TEM),respectively.It is found that using n-butanol as solvent,there is mainly BaTiO₃ with a little BaCO₃ in FBT and BT annealed at 900℃,and there is also a little Ba₂TiO₄ in BT;using ethanol as solvent,there is mainly BaTiO₃ with a little BaCO₃ in BT powders annealed at 900℃,and there is only BaTiO₃ in FBT powders annealed at 900℃,which indicates that FBT annealed at 900℃using ethanol as solvent is purest among all the powders.Two kinds of FBT all have irregular flake-shaped morphology with an average particle size of about 20～40um and the thickness of them is about 3～5um,and two kinds of BT don't have regular shape and symmetrical particle size.Using a coaxial waveguide technique,the complex relative permittivity and permeability of the FBT and BT were measured in the frequency range of 2～18GHz.The RL of FBT/ER composite flat slabs with different mass fractions and thickness of 4mm were tested by reflection/transmission technique,respectively.It is found that the values ofε′andε″for FBT annealing above 700℃all exhibit a clear wave between 8 and 18GHz,and the width of wave becomes broader and broader and the maximum of permittivity becomes bigger and bigger with the increasing temperature,which indicates that FBT can cause high dielectric loss on the high frequency.It is also can be found that the effect of FBT content on the microwave absorption properties and the position of maximum RL peak are great,but the effect of BT content is little.When the weight fraction of FBT increases to 30%,two kinds of FBT/ER composite samples all exhibit better RL performance than BT/ER composite samples,which is because that FBT powders with large surface have large absorption and dispersion section.Moreover,dipoles of big strength are formed in FBT powders.These dipoles have long relaxation time giving rise to dielectric loss and the microwave absorption property.However,the quality of FBT is different due to use different solvents,so it can be found that FBT(using ethanol as soivent)/ER exhibits the best microwave absorption property,and the maximal reflection Joss reaches -9dB at 8.5GHz.