Semiconducting and quartz microbalance (QCM) humidity sensor properties of TiO2 by sol gel calcination method

Titanium dioxide (TiO₂) material was synthesized using the sol gel calcination method. The structural properties of the TiO₂ semiconductor were investigated by atomic force microscopy. The electrical conductivity of the TiO₂ was measured as a function of temperature and TiO₂ exhibits a conductivity of 2.55 × 10⁻⁶ S/m at room temperature with activation energy of 104 meV. The electrical conductivity of the TiO₂ at room temperature is higher than that of nanocrystalline TiO₂ (3 × 10⁻⁷ S/m) and TiO₂ thin film in air (5 × 10⁻⁹ S/m) and in vacuum (8.8 × 10⁻¹⁰ S/m). It was found that the electrical transport mechanism of the TiO₂ is controlled by thermally activated mechanism. The optical band gap of the TiO₂ powder sample was determined to be 3.17 eV, which is good in agreement with the bulk TiO₂ (E_g = 3.2 eV). Up to our knowledge, there is no any reported data about the band gap of TiO₂ nanopowder based on the diffused reflectance calculation. Quartz crystal microbalance (QCM) TiO₂ humidity sensor was prepared. The sensor indicates a large frequency change with an interaction occurred between TiO₂ and humidity molecules. The sensor exhibits a good repeatability when it was exposed to the moist air of 65% RH.