Cu2O doped ZnO as moisture sensor

Paper reports morphological and humidity sensing application of Cu
₂
O doped ZnO composite prepared by solid state reaction. Pellet samples of ZnO-Cu
₂
O nanocrystalline powders with 5, 10, 15 and 20 weight % of Cu
₂
O 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 Cu
₂
O 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.