Influence Of Heat-treatment On Microwave Dielectric Properties Of SiO₂-Al₂O₃-MgO-La₂O₃-ZnO Glass-ceramic System

The glass-ceramic of SiO₂-Al₂O₃-MgO-La₂O₃-ZnO has been chosen as the basicsystem. The transformation of the microwave dielectric properties for this kind ofglass-ceramic has been researched by adjusting the proportion of ZnO as well aschanging heat-treating. The crystallization, dielectric property and microcrystalline phasehave been analyzed by perturbation method combined the XRD and SEM.The results show that the microwave dielectric properties are controlled by theeventual phases existing in the sample after the crystallization period. According to themicrocrystalline phase analysis, as the increase of the ZnO content and the heatpreservation period of 600℃, the proportion of MgSiO₃ and Mg₂La₄Ti₃Si₄O₂₂ phasereduces gradually while the proportion of ZnAl₂O₄ phase increases. According to the dataof the microwave dielectric properties, the dielectric constant is increasing with the ZnOcontent and the temperature coefficient of dielectric constant is decreasing with theprolong of the heat preservation period of 600℃. It can be concluded that the MgSiO₃and Mg₂La₄Ti₃Si₄O₂₂ phase has a lower dielectric constant and a higher temperaturecoefficient while the ZnAl₂O₄ phase has a higher dielectric constant and a lowertemperature coefficient.We acquired samples whose temperature coefficient can situate between 115 and-175ppm/℃by adjusting the ZnO content and the heat preservation period of 600℃. Forexample, one sample(ZnO14wt%, 600℃for 7hrs and then 850℃for 40hrs) has thedielectric properties:ε_r=14.301, Q=1437,Ï„_ε=2.5ppm/℃, and another sample (ZnO15wt%,600℃for 5hrs and then 850℃for 40hrs) has the dielectric properties:ε_r=14.561,Q=1168,Ï„_ε=0.14ppm/℃.