Preparation and characterization of Li+-modified CaxPb1−xTiO3 film for humidity sensor

A novel active element for a humidity sensor based on Ca2+-doped PbTiO3 perovskite ceramic film has been prepared by the sol–gel technique. The addition of alkali ions, especially, Li+ dopant was found to be beneficial to the improvement of the humidity-sensitive characteristic. The resulting film modified by Li+ calcined at 850°C for 1 h was characterized by X-ray diffraction (XRD) and transmission electronic microscope (TEM). The results obtained show that the crystalline size and the lattice distortion are the key factors that influence the humidity properties. At room temperature, and 100 Hz frequency, the variations of sensor’s resistance values (R) are higher than three orders of magnitude over the working relative humidity (ϕ) range, from 8 to 93.5% RH. The curves log R versus ϕ of the designed sensor show excellent linearity, high sensitivity (R8% RH/R93% RH>103), minimal hysteresis (<±2% RH) and rapid response (<8 s).