The Study Of Ceramic/Glass Ceramic Composite Microwave Dielectric Material

In this thesis, a kind of good microwave dielectric glass ceramic,SiO2-MgO-Al2O3-La2O3, is synthesized. And the synthesize and crystallization behavior are investigated. This glass ceramic has low softening point and low dielectric loss crystal phase, and the glass ceramic is mixed with Ba(Mg1/3Ta2/3)O3. After sintering and crystallization, ceramic/glass ceramic composite microwave dielectric material has been prepared. And it is the first time to use this characteristic on purpose. The relationship between microwave dielectric properties and structure are also examined.The method basing on cavity perturbation theory is used to measure the dielectric properties of the composite material. The relative error of this measurement is analyzed, and the data is credible.Crystal temperature of the glass ceramic with 4wt.%B2O3 and 16wt.%TiO2 is about 850 C. The main crystal phases of the glass ceramic are La2Ti2O7 and Al2SiO5. Because there is a compensation between the two main crystal phases, the crystallization doesn't have great effect on the r (dielectric constant) of the glass. And because the solid solution of Mg2+ in crystal phases could reduce the transfer loss of ion, the crystallization effect the Q (quality factor) value greatly. The f (TCF, temperature coefficient of the resonant frequency) of La2Ti2O7 is a large positive value, which result in the negative f of glass before crystallization becomes positive f after crystallization.The addition of glass ceramic could reduce the sintering temperature from 1600 C of pure BMT to 1130 C of the composite dielectric material with the relative density of 92.2%. Appropriate BMT particle size could promote the sintering behavior of the composite material. The BMT fraction shouldn't be more than 60wt.%, otherwise, it would baffle the sinteringprocess obviously.The composite microwave dielectric material specimen sintered at high temperature could get large relative density, which would make the r of the specimen increase with the sintering temperature. With the change of the proportion between La2Ti2O7 and La(Mgo.5Ti0.5)O3, the specimens sintered at high temperature or with fine BMT powder would have large r. The large fraction of La2Ti2O7 at high temperature result in large r.The crystallization degree of glass ceramic controls the Q value of the composite material, and if the glass ceramic hasn't been crystaled completely, the material couldn't obtain high Q value. Even a small fraction of glass will decrease the Q value of the composite material.The f of composite dielectric material is determined by two items. The first is the crystallization degree of glass ceramic in the composite material, and the second is the proportion between La(Mg0.5Ti0.5)O3 and La2Ti2O7 in the glass ceramic after crystallization. Both of them connect with the sintering temperature or the heat treatment.