Effects of ZrO2 on properties of BaO–Al2O3–B2O3–SiO2 composites for LTCC applications

BaO–Al2O3–B2O3–SiO2 (Ba–Al–B–Si) glass containing quartz composites were prepared by the solid state reaction, and the effects of ZrO2 on the microstructure, as well as the mechanical, thermal and dielectric properties were investigated. XRD analysis identified quartz as the major crystal phase, as well as cristobalite and BaSi2O5 as the secondary crystal phases. The source of the cristobalite phase in this composite system is also explained. The results show that in Ba–Al–B–Si composites, ZrO2 as common nucleating agent did not promote the crystallization, but inhibit the precipitation of cristobalite and BaSi2O5 phase; thus ZrO2 can improve the linearity of the thermal expansion and enhance the mechanical properties. However, an excess of ZrO2 addition could worsen the sintering and mechanical behaviors of the Ba–Al–B–Si composites. 5 wt% ZrO2-added Ba–Al–B–Si ceramic specimen exhibited the excellent properties: a high flexural strength (170 MPa), a low dielectric loss (7.5 × 10−4), a low dielectric constant (6.17), and a proper coefficient of thermal expansion (12.36 ppm/°C) with fine linearity.