Cation Substitution for BaTiO3 Phase in Low-Fired Glass-Ceramics for Tunable Microwave Applications

概要

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Cation substitution for the Ba2+ and Ti4+ sites in the BaTiO3 structure was attempted in low-fired glass-ceramics derived from glass powders that have perovskite phase compositions corresponding to $(\text{BaTiO$_{3}$}:\text{REAlO$_{3}$})$ = 9:1 and 8:2 ($\text{RE}=\text{La}$, Nd and Sm) to control the Curie temperature ($T_{\text{c}}$) of the ferroelectric glass-ceramics. The La3+-substituted (9:1) sample heated at 950°C for 24 h showed a broadened $\varepsilon_{\text{r}}$–temperature relationship with substantial lowering in $T_{\text{c}}$ to ${\sim}{-55}$°C. The Ba:La ratio in the perovskite particles was estimated to be in the range of 4:1–6.7:1, whereas very little Al3+ was incorporated into the same particles. It was found that the $T_{\text{c}}$ of the glass-ceramics fabricated in our serial study could be adjusted by A-site cation substitution in BaTiO3. Tailored glass-ceramic samples with room temperature $\varepsilon_{\text{r}}$ of 200–300 and $T_{\text{c}}$ of around 0°C had good microwave tunability of 30–40% under dc bias voltage of 10–50 kV/cm. The high tuning sensitivity of the low-fired glass-ceramics was confirmed by comparative examination of the dielectric properties of well-crystallized ceramics and thin films.
2005-09-15