Study On CaSiO₃-Al₂O₃-based Low Permittivity Microwave Dielectric Ceramics And Its Low Temperature Sintering

Abstract： CaSiO₃-Al₂O₃ceramics were prepared by mixing CaSiO₃andAl₂O₃, and the effects of V2O5, CuO and Li₂CO₃additions on the sinteringproperties, phase compositions, microstructures and microwave dielectricproperties were investigated. The τfof CaSiO₃-Al₂O₃ceramics were adjustedto zero by adding CaTiO₃. The low-fired ceramics could prepare stable slurryand had good compatibility with Ag electrode at900℃. The main researchresults were described as follows:1. The sintering behavior and microwave dielectric properties ofCaSiO₃-Al₂O₃ceramics were investigated systematically. CaSiO₃was addedas sintering aids to decrease the sintering temperature of Al₂O₃ceramics. Theresults revealed that the addition of CaSiO₃into Al₂O₃ceramics resulted inthe emergence of Ca2Al2SiO7and CaAl2Si2O8, which acting as liquidsintering aids could effectively lower the sintering temperature of Al₂O₃ceramics. However, the dielectric constant and the quality value reducedrapidly with the increasing of CaSiO₃addition. On the other hand, Al₂O₃wasadded to improve the density of CaSiO₃ceramics. It was obvious that theAl₂O₃addition resulted in the presence of Ca2Al2SiO7and CaAl2Si2O8, whichcould restrict the growth of CaSiO₃grains by surrounding their boundariesand also improved the bulk density of CaSiO₃ceramics. Sintered at1250℃,1wt%Al₂O₃-doped CaSiO₃ceramic progressed optimal microwave dielectricproperties:r=6.66，Q×f=24,626GHz.2. The sintering temperature of CaSiO₃-1wt%Al₂O₃ceramics with CuO,V2O5and Li₂CO₃additons were effectively decreased to1075℃,1075℃and950℃. The low-fired ceramics progressed good microwave dielectricproperties.3. The sintering temperature of CaSiO₃-1wt%Al₂O₃ceramics withLi₂CO₃and CuO composite additions were effectively decreased to900℃. The low-fired ceramics had good microwave dielectric properties, whichcould prepare stable slurry and had excellent compatibility with Ag electrode.4. CaSiO₃-1wt%Al2O₃powders with1wt%Li₂CO₃and0.2wt%CuOwas synthesized by sol-gel method. Compared to conventional solid-statemethod, the powders synthesized by sol-gel mothod had higher sinteringactivity at900℃and obtained good microwave dielectric properties,r=6.75，Q×f=32,115GHz. CaTiO₃additon was added to adjust the resonancefrequency temperature coefficient of the ceramics to1.25ppm/℃. Thelow-fired ceramics could prepare stable slurry and had excellentcompatibility with Ag electrode.