Effect of rare-earth (RE) ionic radius on the dielectric properties of Sr99%RE1%TiO3 (RE = La, Nd, Yb) single crystals

Abstract

High-performance dielectric materials are essential components of electronic devices. In this work, RE-doped SrTiO₃ (RE = La, Nd, Yb) single crystals with excellent dielectric properties were prepared by the Verneuil method. For La-STO and Nd-STO, the RE ions are substituted for Sr²⁺ only, and the excellent dielectric properties are mainly caused by defect dipoles associated with oxygen vacancies including and defect dipole clusters. For Yb-STO, Yb³⁺ partially replaces Ti⁴⁺, forming an additional defect dipole , resulting in the best dielectric properties (ε′ = 3.6 × 10⁴, tan δ = 0.0036 under 1 kHz). In addition, N₂ atmosphere treatment promotes the production of oxygen vacancies and Ti³⁺ and the formation of more defect dipoles, thus further optimizing the dielectric properties of Yb-STO (ε′ = 4.9 × 10⁴, tan δ = 0.004 under 1 kHz). This work suggests that the dielectric properties of RE-doped SrTiO₃ materials are closely related to oxygen vacancies, and the simultaneous substitution of Sr²⁺ and Ti⁴⁺ should enable obtaining dielectric properties superior to those of the substitution of Sr²⁺ only. The present work provides a clearer understanding of the origin of SrTiO₃ dielectric properties, which is of great significance to the development of SrTiO₃-based dielectric materials.