Composition dependence of colossal permittivity in (Sm0.5Ta0.5)xTi1−xO2 ceramics

Abstract

In this study, colossal permittivity (CP) (10⁴–10⁵) is attained in the (Sm_0.5Ta_0.5)_xTi_1−xO₂ ceramics, and their dielectric loss can be further decreased by doping oxides and optimizing the sintering temperatures. The effects of Sm and Ta as well as the oxides on their microstructure, dielectric properties, and stability were studied in detail. The secondary phases were induced by doping excessive Sm and Ta, and then both backscattering and EDS confirmed that excessive Sm and Ta result in the generation of secondary phases. The relationships between secondary phases and dielectric properties were established. The formation of secondary phases decreases their dielectric constant, whereas their dielectric loss can be slightly decreased through the optimization of Sm and Ta content. In addition, all the ceramics possess an improved frequency (10²–10⁶ Hz) and temperature (−150–200 °C) stability of dielectric properties. Moreover, the addition of oxides containing trivalent (Bi³⁺) or pentavalent (Sb⁵⁺ and Nb⁵⁺) elements can further reduce their dielectric loss. Through the results of XPS, the formation of defect-dipole clusters, e.g., and Ta⁵⁺Ti³⁺A_Ti (A = Ti³⁺/Sm³⁺/Ti⁴⁺), induced by Sm and Ta should be mainly responsible for enhanced dielectric properties.