Control of microwave dielectric properties of CaTiO₃-based high-permittivity ceramics using additives

The effects of Li2O–Bi2O3–TiO2 (LBT) additions on the microwave dielectric properties of high-permittivity CaO–Sm2O3–Li2O–TiO2 (CSLT) ceramics have been investigated. Addition of LBT up to 10 wt % simultaneously reduced the sintering temperature and improved the density of the sintered CSLT ceramics. Scanning electron microscope (SEM) analysis showed a secondary phase when up to 10 wt % of LBT was added to CSLT, which disappeared at higher sintering temperatures. However, x-ray diffraction (XRD) analysis revealed that all the compositions had a distorted perovskite structure. By varying the amounts of LBT additions within 0.5–10 wt % of the main component and the sintering temperature (1200–1400 °C), a wide range of dielectric properties with permittivity in the range of 92–113, Qf≫3000 GHz, and TCf=±20 ppm/°C were obtained. For example, with 1.0 wt % LBT additions sintered at 1400 °C, εr=94.02, Qf=5970 GHz, and TCf=6.8 ppm/°C; with 5.0 wt % LBT add- itions sintered at 1350 °C, εr=101.91, Qf=5050 GHz, and TCf=0.4 ppm/°C; with 10.0 wt % LBT additions sintered at 1250 °C, εr=112.12, Qf=3560 GHz, and TCf=1.0 ppm/°C. These combinations of advantages make LBT a very useful additive in developing a range of dielectric characteristics in CaO–Ln2O3–Li2O–TiO2 group of microwave dielectric ceramics.