Microstructure, colossal permittivity, and humidity sensitivity of (Na, Nb) co‐doped rutile TiO 2 ceramics

Abstract (Na 0.25 Nb 0.75 ) x Ti 1− x O 2 (NNTO) ceramics ( x = 0, 0.005, 0.01, 0.02, and 0.05) were prepared by the conventional solid‐state reaction. The microstructure, dielectric, and humidity sensitivity of the ceramics were systematically investigated. Results showed that all ceramics exhibit pure rutile TiO 2 phase with dense microstructures. Co‐doping of (Na, Nb) can effectively improve the microstructure homogeneity of the ceramics. When the doping level x ≥ 0.01, the co‐doped samples show colossal permittivity higher than 10 4 and dielectric loss tangent lower than 0.38. This dielectric behavior features the merit of both frequency and temperature stability in the range of 10 2 ‐10 6 Hz and 100‐300 K, respectively. The co‐doped ceramics were found to be sensitive to the environment moisture. The humidity sensitivity incurs a Maxwell‐Wagner relaxation near room temperature, which further enhances the dielectric permittivity. Excellent humidity sensitive properties of sensitivity to be 102.6 pF/%RH, response/recovery time to be 115/20 seconds, as well as good repeatability, were achieved in the sample with the doping level x = 0.05. This work underscores that the room temperature dielectric properties of doubly doped TiO 2 system depends strongly on the environmental condition and suggests that the (Na + Nb) co‐doped TiO 2 ceramics might be promising humidity sensing materials.