The Study Of Microwave Dielectric Properties Of SiO₂-Al₂O₃-MgO-La₂O₃ Glass-ceramic System

SiO2-Al2O3-MgO-La2O3 glass-ceramic with high ε r and high Q was prepared by melting method and heat-treating. In the system, the changed mass fraction of BaO(or PbO, or MgO) and different heat-treatment at 850°C made many different samples. The dielectric properties of these samples were measured by perturbation theory. The effect of BaO (PbO, MgO) on the microwave dielectric properties of the glass-ceramic system was investigated.In SiO2-Al2O3-MgO-La2O3 glass-ceramic, BaO can increase ε r . ε r has the max value when the mass fraction of BaO is 4wt%. And the ε r value increases with the increasing of heating time. BaO has no good effect on the system's Q value, because there is BaTiO3 crystal phase.In the SiO2-Al2O3-MgO-La2O3 glass-ceramic, PbO also can increase ε r . The ε r value of the samples with PbO after long-time heat-treatment is bigger than 14. And the max value of ε r is 16.29, when the mass fraction of PbO is 14wt% and the time of the treatment is 72 hrs. After long-time heat-treatment, the main crystal phase of the system is Mg2La4Ti3Si4O22 (monoclinic). Pb9AlgO2i makes the max ε r value, when PbO wt%=14wt%. In the heat-treatment process, the change of Q is not a gradually increasing process. There is the right heat-treatment that makes Q reach a large value. The main phase Mg2La4Ti3Si4O22 makes the system mostly have negative τ f. But PbB4O7 phase has the positive τ fWith increasing of the mass fraction of TiO2 , the crystallization of the system is quickened. After the heat-treatment at 850°C for 30 hrs, the crystallization of the system is almost completed. MgO have good effect on the dielectric constant. When the mass fraction of MgO is less than 14wt%, the dielectric constant increases with the increasing of the mass fraction of MgO. After long-time heat-treatment, the Q value of all the samples is larger than 2600.The dielectric properties of Mg2La4Ti3Si4O22 (f=10 Ghz) are, ε r= 14.86,...