DFT calculations and giant dielectric responses in (NiNb)TiO.

The origins of dielectric responses in Ni and Nb co-doped TiO were explored considering intrinsic and extrinsic effects. DFT calculations demonstrated that Ni doping induced oxygen vacancies, while Nb doping generated free electrons. Theoretical predictions indicated complex defect dipoles forming in the rutile structure, contributing to overall dielectric responses. Theoretical calculations also showed a possible linear alignment of Ni-2Nb without oxygen vacancies, especially in high doping concentrations. Experimentally, (NiNb)TiO ceramics ( = 1%, 2.5%, and 10%) were synthesized. The substantial dielectric response at room temperature, attributed to factors like defect dipoles and grain boundary/surface barrier layer capacitor (GBLC/SBLC) effects, increased with higher doping levels. However, in a temperature range where GBLC/SBLC effects were suppressed, the dielectric response decreased with increased doping, likely due to self-charge compensation between Ni-2N. Notably, (NiNb)TiO with = 2.5% exhibited a high dielectric permittivity of 10 and a low loss tangent of 0.029 at 1 kHz. Moreover, the dielectric permittivity changed by less than ±15% (compared to 25 °C) at 150 °C. This work provides an understanding of the origins of dielectric responses in co-doped TiO and optimizes the doping concentration to achieve the best dielectric performance.