Influence of Li2CO3 additions to CaSiO3–Al2O3 ceramics on sintering temperature and microwave dielectric properties

摘要

The effects of Li₂CO₃ additions on the densification and microwave dielectric properties of CaSiO₃–1 wt % Al₂O₃ ceramics were investigated. With Li₂CO₃ addition, the densification temperature of CaSiO₃–1 wt % Al₂O₃ ceramics could be effectively reduced from 1250 to 925°C. During the sintering process, Li₂CO₃ existed as a liquid phase and assisted the densification of CaSiO₃–1 wt %Al₂O₃ ceramics, and then reacted with CaSiO₃ to form Li₂Ca₃Si₆O₁₆ and Li₂Ca₄Si₄O₁₃ second phases. However, the Li₂CO₃ addition deteriorated the microwave dielectric properties because of the lower quality values of Li₂Ca₃Si₆O₁₆ and Li₂Ca₄Si₄O₁₃ phases. The proper Li₂CO₃ addition was found to be 2 wt %. Under this addition, microwave dielectric properties of ε _r = 7.33, Q × f = 21,904 GHz and τ _f = ?34 ppm/°C were obtained for the CaSiO₃–1 wt % Al₂O₃ ceramic sintered at 975°C for 2 h.