Role of trivalent acceptors and pentavalent donors in colossal permittivity of titanium dioxide ceramics

Abstract

Acceptor and donor co-doped titanium dioxide (TiO₂) materials have a colossal permittivity (CP), a low dielectric loss, and a good temperature/frequency stability, showing an immense potential for microelectronics and high-energy storage devices. In this study, we propose to decode the role of acceptors and donors on CP dielectric properties in TiO₂ by doping a series of A³⁺ acceptors or B⁵⁺ donors. A reduced dielectric loss of tan δ < 0.10 with small permittivity is observed in A³⁺-TiO₂, whereas a CP with ε_r > 10⁵ is displayed in B⁵⁺-TiO₂ accompanied by a high dielectric loss (>0.40). Both of them possess an obvious temperature/frequency sensitivity. Inversely, an additive effect with CP and low dielectric loss appears in A³⁺ and B⁵⁺ co-doped TiO₂ over a broad temperature/frequency range, e.g., a giant ε_r value (5.7–9.6 × 10⁴) and a low tan δ value (0.05–0.096) are achieved in a paradigm system of (Gd_0.5Nb_0.5)_xTi_1−xO₂. The XPS analysis indicates that introducing A³⁺ causes the appearance of , while the B⁵⁺ substitution can afford an extra electron to transform Ti⁴⁺ to Ti³⁺. The introduced cations and generated defects combine together to form an electron-pinned defect-dipole and cause a strong dipole polarization. These defects can also facilitate the internal barrier layer capacitance and surface barrier layer capacitor effects, leading to a higher CP property.