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

Abstract

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 (BaTiO3:REAlO3) = 9:1 and 8:2 (RE=La, Nd and Sm) to control the Curie temperature (Tc) of the ferroelectric glass-ceramics. The La3+-substituted (9:1) sample heated at 950°C for 24 h showed a broadened εr–temperature relationship with substantial lowering in Tc to ∼-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 Tc 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 εr of 200–300 and Tc 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.