Phase development and dielectric properties of BaAl₂Si ₂O₈-based low temperature co-fire ceramic material

Low-temperature co-fired ceramics (LTCC) is a glass-ceramic composite, in which the glass crystallization occurs during firing. The amount and type of the crystalline and amorphous phases determine the final properties. A commercial glass-ceramic powder was selected in this study. The phase development was studied by XRD, the thermal properties were studied by DTA and dilatometry. The dielectric properties were measured by the Hakki and Coleman method. The results show that Al₂O₃, TiO₂, and Zn ₂SiO₄ existed in the as-received powder and their quantities decreased as the firing temperature increased. BaAl ₂Si₂O₈ appeared at 850°C and its quantity increased with temperature. At 900°C, Sr₂Al₂SiO ₇, and (K_0.94Na_0.06) (Al_0.99Si _3.01)O₈ were formed. The degree of crystallinity of the as-received powder was around 53 mass % and gradually increased, reaching a maximum of ∼96 mass% at 900°C. As the firing temperature increased, the dielectric constant of the fired specimens decreased, but the quality factor increased. The decrease in dielectric constant can be attributed to the porous microstructure and the increase of the quality factor can be attributed to the increasing degree of crystallinity at high temperatures. However, the porous microstructure deteriorates the mechanical strength of the fired specimens. So a trade-off between the dielectric properties and the mechanical strength should be made.