Effect of limited current on ultrarapid densification and giant dielectric properties of flash sintering (La, Ta) co-doped TiO₂ ceramics

Flash sintering is considered a promising energy-saving and efficient technology for preparing high-temperature ceramics. The effects of limited current on flash sintering parameters, microstructure, and electrical properties of (La_1/2, Ta_1/2)_0.02Ti_0.98O₂ ceramic were investigated by the XRD, SEM, XPS, and precision impedance analyzer. With limiting current increase, the grain size of flash sintering sample increases gradually, and the relative density increases first and then decreases. The average grain size is about 1 μm, and the highest relative density is 96.9%. Joule heating runaway and oxygen vacancy defect lead to rapid densification of flash sintering La and Ta co-doped TiO₂ ceramics. According to the EPDD model, doped La³⁺ and Ta⁵⁺ ions increase the concentration of oxygen vacancies and free electrons, lead to local polarization of carriers, and obtain a giant dielectric constant of ε^’ = 7.6 × 10⁴ and low dielectric loss of tanδ = 0.11. At high temperature, electrons break free from the constraints of defect clusters and accumulate at the interface, leading to interface polarization due to the IBLC model. The giant dielectric properties originate from the combined effect of EPDD and IBLC model.