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

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 A(3+) acceptors or B5+ donors. A reduced dielectric loss of tan < 0.10 with small permittivity is observed in A(3+)-TiO2, whereas a CP with epsilon(r) > 10(5) 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 A(3+) and B5+ co-doped TiO2 over a broad temperature/frequency range, e.g., a giant epsilon(r) value (5.7-9.6 x 10(4)) and a low tan value (0.05-0.096) are achieved in a paradigm system of (Gd0.5Nb0.5)(x)Ti1-xO2. The XPS analysis indicates that introducing A(3+) 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.