Low-firing of CaAl2B2O7 ceramics with Li2O–B2O3–SiO2 and LiF additions

Abstract

Lithium borosilicate (LBS) and lithium fluoride (LiF) are verified to be effective sintering aids for CaAl2B2O7 microwave dielectric ceramic to reduce the sintering temperature and lower the activation energies. Benefiting from the liquid phase sintering, low-firing, low permittivity and low-loss CaAl2B2O7 microwave dielectric composite has been successfully obtained. Typically, CaAl2B2O7 assembled with 1 wt % LBS composite possesses desirable properties of εr = 5.91, Q × f = 39,443 GHz, τf = −23.51 ppm/°C (@16.53 GHz). For composite ceramics with 0.5 wt % LiF, the optimal microwave dielectric properties are εr = 6.08, Q × f = 37,295 GHz, τf = −22.39 ppm/°C (@15.78 GHz). The two kinds of composite are densified at 875 °C, with co-existed CaB2O4 and liquid phase. The mechanism underlying the low temperature sintering is revealed by well-matched wettability and lower activation energy of composite ceramics with additions.