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 10wt% 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 10wt% 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 0.5–10wt% 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>3000GHz, and TCf=±20ppm∕°C were obtained. For example, with 1.0wt% LBT additions sintered at 1400°C, εr=94.02, Qf=5970GHz, and TCf=6.8ppm∕°C; with 5.0wt% LBT additions sintered at 1350°C, εr=101.91, Qf=5050GHz, and TCf=0.4ppm∕°C; with 10.0wt% LBT additions sintered at 1250°C, εr=112.12, Qf=3560GHz, and TCf=1.0ppm∕°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.