Fine-grain induced ultrahigh energy storage density and fast discharge speed in novel Bi0.5K0.5TiO3–Ba(Mg1/3Nb2/3)O3 ceramics via a hot-pressing strategy.

Nanomaterials of TiO 2 , (K 0.5 Na 0.5 )NbO 3 , and the TiO 2 / (K 0.5 Na 0.5 )NbO 3 nanocomposite were successfully synthesized by a hydrothermal method. Impedance-type humidity sensors were fabricated based on these materials. Our results reveal that the impedance of the TiO 2 /(K 0.5 Na 0.5 )NbO 3 sensor changes by 5 orders of magnitude with an ultrahigh sensing response of S f = 166 470 recorded at 100 Hz in the tested relative humidity (RH) range of 12− 94%. This value is almost 2 and 4 orders of magnitude larger than that of the (K 0.5 Na 0.5 )NbO 3 and TiO 2 sensors, respectively. Interestingly, satisfactory response/recovery time (25/38 s, within 5 min), very small hysteresis (<5%), excellent stability, and good repeatability were also achieved in the TiO 2 / (K 0.5 Na 0.5 )NbO 3 sensor. The improved sensing properties are ascribed to the synergistic effect of TiO 2 /(K 0.5 Na 0.5 )NbO 3 heterojunction, which contributes the impedance that is susceptible to environmental humidity. This work underscores that it is a facile way to boost humidity-sensing performance by constructing proper nanocomposites.

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(Na0.25Nb0.75)xTi1−xO2 (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 TiO2 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 104 and dielectric loss tangent lower than 0.38. This dielectric behavior features the merit of both frequency and temperature stability in the range of 102‐106 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 TiO2 system depends strongly on the environmental condition and suggests that the (Na + Nb) co‐doped TiO2 ceramics might be promising humidity sensing materials.

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