Oxidation Mechanism of Cu2O and Defect Structure of CuO at High Temperatures

Abstract

Kinetics and mechanism of Cu 2 O oxidation have been studied as a function of temperature (973-1273 K) and oxygen pressure (1-10 5 Pa), using microthermogravimetric and marker techniques. It has been found that in early stages not exceeding 30 hours, CuO formation follows approximately cubic rate law and in later stages, the process can be described by parabolic kinetics with the rate being independent of Cu 2 O pretreatment. Marker experiments, confirmed by two-stage oxidation studies, have demonstrated that the growth process of CuO layer on the surface of Cu 2 O proceeds by the outward diffusion of cations, clearly indicating that the cation sublattice of CuO is predominantly defected. These results together with kinetic and nonstoichiometry data strongly suggest that in addition to intrinsic electronic disorder (i.e. electron holes and quasi-free electrons), doubly ionized cation vacancies are the prevailing ionic defects in this oxide.