Effect of V2O5 doping on p- to n-conduction type transition of TiO2:WO3 composite humidity sensors

Abstract

Actually, humidity sensors have got multiplying applications from the industrial processing to the environmental control, mainly those based on semiconducting metal oxides. Certain ceramic oxides or composite oxides are wide-bandgap semiconductors and the overall conduction mechanisms are highly influenced by the sensing material physical/chemical properties. For the humidity measurement (relative humidity (RH)), the electronic/ionic charge transfer reactions that take place at the semiconductor surface can be used for this purpose.It is well recognized that water molecules are observed to increase the conductivity of n-type ceramics and to decrease the conductivity of p-type ceramics. Nevertheless several mechanisms have been proposed to explain electrical response variations of oxide metals of with humidity.The present paper describes part of the work that is being carried out to investigate the effect of doping metals oxides on TiO2:WO3 bulk sensors humidity response.For that the V2O5 ceramic was selected. The influence of different contents, 3, 5 and 7 percentage in weight, were investigated concerning microstructural characterization and their electrical response was measured in the range 400Hz–40MHz, at operating temperatures of 20 and 30°C and on the relative humidity (RH) range between 10 and 100%. For all doped sensors a p- to n-conduction transition was found, and the best humidity response was observed for the sensor containing 3 percentage in weight of oxide doping. Besides a new non-classical model for the doped sensors electrical behaviour with moisture is depicted, which allow to better comprehend the diverse phenomena present in our sensors contributing to the overall electrical response.