Low sintering temperature enhancing colossal dielectric permittivity and humidity sensitivity in Ta substituted TiO ceramics via high energy ball milling.

Nanostructured 1% and 10% Ta⁺-substituted TiO (TTO) ceramics were synthesized via high-energy ball milling and sintered at 1200 °C and 1300 °C to investigate their dielectric and humidity sensing performance. XRD confirmed a single-phase rutile TiO structure in both the powdered and sintered ceramics, while SEM and EDS analyses revealed dense microstructures with nanoscale grains and uniform Ta⁺ dispersion, particularly at the lower sintering temperature. The 10%TTO ceramic sintered at 1200 °C exhibited colossal dielectric permittivity (ε' ≈ 1.3 × 10) with a relatively high loss tangent, whereas both 1%TTO and 10%TTO sintered at 1300 °C achieved similarly high ε' values with significantly reduced dielectric loss (tan δ ≈ 0.026 at 1 kHz). Excellent thermal stability was maintained, with Δε' <  ± 15% and tan δ < 0.1 up to 200 °C. Furthermore, ceramics sintered at 1200 °C demonstrated outstanding humidity sensing behavior, including high linearity, low hysteresis (γ = 3.0%), and rapid response/recovery times (3.0/0.5 min). These exceptional properties are attributed to the nanoscale microstructure and defect-mediated intrinsic factors at the ceramic surface. The synergy of colossal dielectric permittivity, excellent temperature stability, and superior humidity sensitivity highlights the potential of Ta⁺-substituted TiO ceramics as promising candidates for advanced capacitors and humidity sensors, with performance tunable by sintering conditions.