Enhanced humidity sensing properties of Ta2O5 and ITO doped rutile-TiO2 porous ceramics

In this study, we investigated the humidity sensing properties of TiO₂-based ceramics doped with tantalum pentoxide (Ta₂O₅) and indium tin oxide (ITO). Pure TiO₂, 1%Ta-doped TiO₂ (1%TTO), 1%ITO-doped TiO₂ (1%ISTO), and 1%(Ta₂O₅ + ITO) co-doped TiO₂ (1%ISTTO) ceramic samples were obtained by sintering at 1200 °C for 3 h. The rutile phase was observed in all samples. The lattice parameters of the single and co-doped samples were larger than those of pure TiO₂, confirming the substitution of dopants. Porosity was observed in all ceramics. The mean grain sizes of all doped samples were significantly reduced compared to undoped TiO₂. A homogeneous element dispersion was observed in the 1%TTO and 1%ISTTO ceramics, while segregation particles of related In-rich elements was observed in the 1%ISTO ceramic. Giant dielectric properties were not achieved in any samples due to the porosity. Nevertheless, excluding the undoped TiO₂, the dielectric properties of all porous ceramics varied significantly with changes in humidity. The 1%ISTTO ceramic demonstrated superior humidity sensing properties, including a low maximum hysteresis error of 3.6% at 10² Hz. In contrast, the 1% TTO and 1% ISTO ceramics showed higher maximum hysteresis errors of 7.2% and 19.8%, respectively. Notably, the response and recovery times were 7.05 ± 0.18 and 2.48 ± 0.39 min, respectively, with good repeatability. This improvement is likely due to the synergistic effect of oxygen vacancies and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mtext>Ta</mml:mtext> <mml:mrow><mml:mtext>Ti</mml:mtext></mml:mrow> <mml:mo>·</mml:mo></mml:msubsup> </mml:math> defects on the surface, enhancing the humidity sensing properties of the 1% ISTTO ceramic, coupled with its optimal microstructure due to its lowest porosity and grain size.