Air quenching as a reliable technique to obtain colossal dielectric constant with low loss in (In, Nb)-co doped TiO2

•The unique electrical properties were obtained in air quenched co-doped TiO2.•By quenching, εr enhanced from 21*103 to 26*104 and tanδ decreased from 0.6 to 0.1.•Air quenched sample had a lower Eb than the furnace cooled sample.•The mechanism of EPDD was activated by air quenching and contributed to EP and IBLC. In this research, for the first time, the effect of air quenching on the microstructural and electrical properties of (In, Nb) co-doped TiO2 was investigated. The FE-SEM images showed that the air quenching has no effect on microstructure of co-doped TiO2. However, air quenching affected the electrical properties so that the dielectric constant in the frequency of 1 kHz at room temperature sharply enhanced from 21*103 to 26*104 and the dielectric loss surprisingly decreased from 0.6 to 0.1. This incredible improvement in the dielectric properties is attributed to the electron-pined defect dipoles which has been activated through air quenching.