Oxygen-vacancy-related dielectric relaxations and electrical properties in [Lix(BaSrCaMg)(1−x)/4]TiO3 high-entropy perovskite ceramics

High-entropy perovskite ceramics, [Lix(BaSrCaMg)(1−x)/4]TiO3 (x = 0.1, 0.15, 0.2, 0.3), were designed and successfully synthesized by solid-state method. The effects of Li contents on the phase formation, microstructures, and the origin of dielectric relaxation of all ceramics have been systematically investigated. The results show that all ceramics exhibit perovskite structure, and increasing Li content is conducive to grain growth and the formation of dense ceramics. XPS and EPR prove that oxygen vacancies increase with the increase of Li content. It is observed at room temperature that the increase of Li content not only contributes to the improved permittivity but also results in high-dielectric loss. Two sets of dielectric relaxations are observed in all ceramics. The lower temperature relaxation is shown to originate from the interfacial polarization, while the higher temperature relaxation is ascribed to double-ionized oxygen vacancies. The rapid increase of permittivity at higher temperatures and lower frequencies can be explained by space charge related to oxygen vacancies.