Microstructure, Thermal, Mechanical, and Dielectric Properties of BaO-CaO-Al2O3-B2O3-SiO2 Glass-Ceramics

BaO-CaO-Al2O3-B2O3-SiO2 (BCABS) glass-ceramics were prepared via the method of controlled crystallization. The effect of CaO modification on the microstructure, phase evolution, as well as thermal, mechanical, and dielectric properties was investigated. XRD identified that quartz is the major crystal phase; cristobalite and bazirite are the minor crystal phases. Moreover, the increase of CaO could inhibit the phase transformation from quartz to cristobalite, but excessive CaO would increase the porosity of the ceramics. Additionally, with increasing the amount of CaO, the thermal expansion curve tends to be linear, and subsequently the CTE value decreases gradually, which is attributed to the decrease of cristobalite with high CTE and the formation of CaSiO3 with low CTE. The results indicated that a moderate amount of CaO helps attaining excellent mechanical, thermal, and dielectric properties, that is, the specimen with 9 wt% CaO sintered at 950 degrees C has a high CTE value (11.5 x 10(-6)/degrees C), a high flexural strength (165.7 MPa), and good dielectric properties (epsilon(r) = 6.2, tan delta = 1.8 x 10(-4),. = 4.6 x 10(11) Omega.cm).