Electrical Properties of TiO2-K2Ti6O13 Porous Ceramic Humidity Sensor

Porous ceramic humidity sensors using pure TiO2 doped with a few molar percent K2CO3 were studied. The conductance versus relative humidity (rh) sensitivity of the sensor sintered at 1200°C was as high as 4 orders of magnitude in the range of 15% to 95% rh at 200 Hz and 25°C. The sensors were reversible without repeated high‐temperature thermal desorption processes. The electrical properties of the sensors under different rh were determined by both direct current (dc) and alternating current (ac) analysis techniques. The sensors could be polarized similar to electrolytes in a charging process as a result of the electrode and water molecular polarization effects, and the effects were enhanced with increasing rh. The conduction carriers of the sensors in a moist atmosphere were ions and electrons, and the dominant conduction carrier was ions. By complex impedance plots with a “non‐Debye” capacitor concept, an equivalent circuit model was established which can simulate well all the electrical properties of the sensors in the range of 65% to 95% rh for all measured frequencies (5 Hz to 13 MHz). The relative dielectric dispersion k’(ω) increased with increasing rh and was almost proportional to ω−1.85 at low frequencies. The relative dielectric absorption k″(ω) increased with increasing rh and was almost proportional to ω−1 at low and median frequencies.