Effect of Al–Nb codoping on dielectric properties and breakdown strength of rutile TiO₂ ceramics

Acceptor–donor codoping is gaining attention as a novel method for enhancing the intrinsic dielectric permittivity of TiO2 ceramics. Aiming at the application of TiO2 in high-voltage multilayer ceramic capacitors, this study investigated the dielectric properties and breakdown strength of TiO2 ceramics doped with equimolar amounts of Al3+ and Nb5+ ions at a total doping concentration of up to 10.0 mol %. The dielectric permittivity was not increased by the codoping, but gradually decreased with increasing the codoping concentration. Meanwhile, a small amount of Al–Nb codoping (up to 2.0 mol %) suppressed dielectric loss at both room and elevated temperatures. The dielectric breakdown field was also significantly improved at up to 5.0 mol % codoping concentrations. The effects of Al–Nb codoping on the dielectric properties and breakdown strength are discussed in terms of microstructure, defect concentration, and mobility of charged oxygen vacancies.