Colossal permittivity characteristics and mechanism of (Sr, Ta) co-doped TiO₂ ceramics

Colossal permittivity (CP) materials have great application prospects in electronic devices. However, obtaining a giant dielectric constant, low dielectric loss, and good temperature stability in one phase simultaneously is a challenge. In this work, the colossal permittivity characteristics along with the related mechanism of (Sr, Ta) co-doped TiO₂ ceramics were investigated. According to the dielectric analysis, the dielectric properties are significantly improved when Sr and Ta co-doped, where the addition of Sr is responsible for the reduced tan δ, and the addition of Ta is responsible for the improved ε′. The enhanced dielectric constant (> 10⁵) with relatively low dielectric loss is obtained in a large substitution range from x = 1 to 7%, and the good frequency and temperature stability are observed in these samples. In addition, the optimum dielectric properties are obtained at x = 0.05, where ε′ = 1.86 × 10⁵, tan δ = 0.15. XPS analysis confirms the existence of reduced Ti³⁺ ions and oxygen vacancies, which may form the highly stable defect clusters. The defect clusters are responsible for the improved dielectric properties in (Sr, Ta) co-doped TiO₂ ceramics. Meanwhile, the interfacial polarization is mentioned to explain CP phenomenon of TiO₂-based ceramics. This research is conducive to the development and application of TiO₂-based new CP materials.