Low-temperature dielectric relaxation and microwave-terahertz dielectric response of Ca-Sm-Ti-O perovskite ceramics

Low-loss (high-Q×f, where Q = 1/tan δ) dielectric ceramics can help achieve efficient microwave signal transmission and reduce heat generation. In the traditional Ca-Ln-Ti-O perovskite system (where Ln = rare earth) with the general formula of Ca_1–xLn_2x/3TiO₃ (CSTx), the sharp decline in the Q×f value when x > 0.5 remains unexplained, posing a challenge for designing low-loss ceramics. In this study, CSTx ceramics (x ≤ 0.7) are synthesized via the solid-state reaction method, with a focus on their structure, defects, and broadband dielectric properties. A significant discrepancy between the Q×f values in the microwave and terahertz bands is found when x ≥ 0.6, suggesting the presence of additional loss mechanisms in the microwave band beyond ion displacement depolarization. Meanwhile, the low-frequency dielectric spectra show a weak dielectric relaxation in the low-temperature region, attributed to the partially ordered A-site vacancies. Therefore, this relaxation can act on the microwave frequency band at room temperature, resulting in a sharp decline in Q×f values. Such low-frequency and low-temperature dielectric relaxation should not be ignored in the research of microwave dielectric ceramics. These findings provide a crucial theoretical reference for developing low-loss microwave dielectric ceramics.