LAUSR

Abstract The influences of sintering temperature on the microstructure and giant dielectric properties of a new co-doped TiO 2 system, i.e. , V and Ta co-doped TiO 2 , were investigated. The grain size of (V 1/2 Ta 1/2 ) 0.01 Ti 0.99 O 2 ceramics was enlarged with increasing sintering temperature. Dense microstructure and homogeneous dispersion of dopants were achieved in the ceramics sintered at 1400–1500 °C for 5 h. The dielectric permittivity in the frequency range 40–10 6  Hz of the (V 1/2 Ta 1/2 ) 0.01 Ti 0.99 O 2 ceramics significantly increased with the mean grain size, while the dielectric loss tangent was reduced to 0.033 at 10 2  Hz. Furthermore, the high-temperature stability of the dielectric permittivity was improved with increasing mean grain size. The electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries and/or surface layers was confirmed using impedance spectroscopy. The conduction inside the semiconducting grains was attributed to electron hopping between Ti 4+ and Ti 3+ , which was confirmed by X-ray photoelectron spectroscopy. Very high resistivity with a large conduction activation energy of the insulating parts was suggested as the primary cause of the giant dielectric permittivity with low loss tangent.