Greatly enhanced humidity sensing performance 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 y Ta 0.025 Ti 0.975-y O 2 ( y %ScTTO) ceramics with varying Sc 3+ concentrations (1 %, 2.5 %, and 5 %). The ceramics were synthesized using a solid state reaction method. X ray diffraction analysis confirmed the presence of the main rutile TiO 2 phase without any impurity phases. The ceramics exhibited a high density microstructure with a relative density exceeding 92 %. The mean grain size increased with higher Sc 3+ 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 Sc rich phase along the grain boundaries. All samples demonstrated a giant dielectric constant of 10 3 –10 5 , which decreased as the Sc 3+ 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.