Nonstoichiometry and Chemical Diffusion in Co3O4 Cobalt Oxide

Nonstoichiometry and chemical diffusion in Co 3 O 4 oxide have been studied as a function of temperature (973-1173 K) and oxygen pressure (30-10 5 Pa), using thermogravimetric techniques. It has been found that at very low oxygen pressures, close to the dissociation pressure of the oxide, interstitial cations and quasi-free electrons are the predominant point defects, while at high pressures cation vacancies and electron holes predominate. This behaviour is reflected in complex dependence of the deviation from stoichiometry, y, in the Co 3±y O 4 oxide on oxygen pressure. At low pressures, namely, deviation from stoichiometry decreases with increasing oxygen pressure, reaching virtually constant value in intermediate pressures and increases at highest pressure range. Finally, these data as well as the results of kinetic rate measurements of Co 3±y O 4 formation have been utilized in calculating the chemical diffusion coefficient as a function of temperature.