Cu2O doped ZnO as moisture sensor

Paper reports morphological and humidity sensing application of Cu₂O doped ZnO composite prepared by solid state reaction. Pellet samples of ZnO-Cu₂O nanocrystalline powders with 5, 10, 15 and 20 weight % of Cu₂O in ZnO have been prepared. These pellets have been annealed at temperatures 200-500°C. When samples have been exposed to humidity, it has been observed that as relative humidity increases, resistance of the pellet decreases for the entire range of humidity from 10% to 90%. The sample with 20% of Cu₂O doped in ZnO shows best results with sensitivity of 4.23 M¿/%RH when annealed at 500°C. This sensing element manifests lower hysteresis, less effect of ageing and high reproducibility for annealing temperature 500°C. For this sensing element the two values of activation energy corresponding to two slopes in Arrhenius plot are 0.0274 eV for the temperature range 200-400°C and 0.0839 eV for the temperature range 400-500°C. XRD pattern shows peaks of hexagonal zincite and monoclinic tenorite. As calculated from Scherer´s formula the particle size for this sensing elements is 119 nm and according to SEM micrograph 104 nm.