ELECTRON-PARAMAGNETIC RESONANCE STUDY OF THE INTERACTION OF THE ZNO SURFACE WITH AIR AND AIR REDUCING GAS-MIXTURES

The variation of the defect number that results from the interaction of ZnO with air-reducing gas mixtures (H-2-air and CO-air) has been investigated by EPR spectroscopy. It appears that up to 573 K the surface interaction with CO or H-2 and air is dominated by the reaction of CO or H-2 with the chemisorbed oxygen species (O2- and O-); at higher temperature the main process is the formation of new oxygen vacancies. The CO effect is stronger than that of H-2 up to 573 K; after this temperature the relative importance reverses and H-2 is more efficient than CO in producing new oxygen vacancies.