Physical behaviour of BaTiO3–CuO thin-film under carbon dioxide atmospheres

A theoretical model explaining the CO2 sensing mechanism of BaTiO3–CuO thin-films is presented. This model is based on the work function variations of the p–n heterojunction that exists between BaTiO3 (n-type) and CuO (p-type). Impedance measurements are carried out at different carbon dioxide concentrations in order to check the theory exposed and also to show that the Ag as an additive improves the sensor response because a metal–semiconductor junction appears between the silver and the sensing material. Response to CO2 at different working frequencies and the relation between response and the spatial-charge and relaxation phenomena are also presented.