Microwave and infrared dielectric properties of Sr1−3x/2CexTiO3(x = 0.154–0.400) incipient ferroelectrics at cryogenic temperatures

Abstract

Sr1−3x/2CexTiO3 (x = 0.154–0.400) or Sr2+nCe2Ti5+nO15+3n (n ≤ 8) ceramics were prepared by the mixed oxide route. The microwave (MW) dielectric properties of the compounds were investigated in the temperature range from 8 to 295 K. The permittivity increases for decreasing temperatures and saturates below 30 K, following Barrett's equation, demonstrating the incipient ferroelectric nature of the investigated materials. The dielectric loss tangent decreases for decreasing temperatures, reaching a minimum at about 80–120 K, and again increases with further cooling due to the rotations of TiO6 octahedra. Infrared-reflectivity data show that the dielectric response of the system is driven by the lowest-frequency polar (soft) mode, particularly at lower temperatures, where the phonons become practically uncoupled. The results help us to understand why Sr1−3x/2CexTiO3 materials present more appropriate dielectric properties for MW tunable applications, compared with pure SrTiO3.