Greatly Enhanced Humidity Sensing Performances with Ultra Low Hysteresis Error in Giant Permittivity TiO2 Ceramics Co–doped with Sc3+ and Ta5+ Ions

This study investigates the dielectric and humidity sensing properties of Sc_yTa_0.025Ti_0.975-yO₂ (y%ScTTO) ceramics with varying Sc³⁺ concentrations (1%, 2.5%, and 5%). The ceramics were synthesized using a solidstate reaction method. Xray diffraction analysis confirmed the presence of the main rutile TiO₂ phase without any impurity phases. The ceramics exhibited a highdensity microstructure with a relative density exceeding 92%. The mean grain size increased with higher Sc³⁺ doping concentrations. Elemental mapping showed homogeneous dispersion in the 1%ScTTO and 2.5%ScTTO samples, while the 5%ScTTO sample exhibited segregation of a Scrich phase along the grain boundaries. All samples demonstrated a giant dielectric constant of 10³–10⁵, which decreased as the Sc³⁺ concentration increased. Notably, the 1%ScTTO and 2.5%ScTTO samples displayed significant humidity sensitivity. The capacitance of these samples increased by 100% and 1700%, respectively, as the relative humidity increased from 30 to 90%. Remarkably, the 2.5%ScTTO sample exhibited minimal hysteresis error, measured at 1.09% at 1 kHz. Furthermore, these samples showed very fast response and recovery times, ∼1 and 0.15 min, respectively. The humidity sensing properties at 1 kHz and 25 °C remained stable under a DC bias of up to 12 V but showed a significant increase when the temperature was raised to 50–75 °C (without DC bias). The enhanced humidity sensing performance and giant dielectric response were attributed to the formation of defects and the grain boundary effect.