Effect of Ta2O5 addition on the structure, crystallization mechanism, and properties of CaO–B2O3–SiO2 glasses for LTCC applications

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CaO–B2O3–SiO2–Ta2O5 (CBST) glass-ceramics, with different Ta2O5 content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta5+ to the oxygens in the BO33− and SiO32− structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta5+, which results in a weakening of the vibration intensities of the [BO3] and [SiO4] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (Tg), crystallization starting temperature (Tc1), and exothermic crystallization peak temperature (Tp1), of the CaSiO3 phase, shifted to higher values with the addition of Ta2O5. Also, the crystallization activation energy (Ea) and the glass stability factor (ΔT) of the CaSiO3 phase increased, which indicated that the CaSiO3 phase of the glass became inhibited by the addition of Ta2O5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta2O5, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta2O5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: εr = 6.22 and tanδ = 1.19 × 10−3 (1 MHz). To sum up, CaO–B2O3–SiO2–Ta2O5 glass-ceramics are potential low temperature co-fired ceramic substrate materials.