Oxidation of Cobalt at High Temperatures and Self-Diffusion in Cobaltous Oxide

Application of Wagner's Theory to the Parabolic Growth of Oxides Containing Different Kinds of Defects: I . Pure Oxides

“…Neutral, singly, and doubly charged metal vacancies are present in CoO, their concentration being a function of the prevailing oxygen activity under a constant temperature. Around 1000~ and at high oxygen activities the vacancies are prevailingly singly charged (12,16,21,(47)(48)(49)(50)(51)(52), in agreement with the value of the oxygen pressure exponent in the dependence of the parabolic rate constant, the deviations from stoichiometry, and the self-diffusion coefficient of Co on P (02) (16,21,. Diffusion of oxygen is instead unimportant in this oxide (56).…”

“…The high temperature oxidation of cobalt has been studied frequently so far (9)(10)(11)(12)(39)(40)(41)(42)(43)(44)(45)(46), like the defect structure (12,16,20,21,(47)(48)(49)(50)(51)(52) and the diffusion properties of CoO (9,12,16,21,(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). There is a general agreement that Co oxidizes according to a parabolic rate law at high temperatures, the process being controlled by the diffusion of metal vacancies in the p-type semiconducting oxide (39)(40)(41)(42)(43)(44)(45)(46).…”

“…In addition to metal vacancies, Co interstitials have been proposed as minority defects to explain the effect of Li doping on the electrical properties of CoO (61) and the difference between the concentration of defects deduced from the deviations from stoichiometry and that obtained from measurements of the oxidation rate of cobalt (21,52). Metal interstitials have also been found by x-ray diffraction in solid solutions CoO-NiO (20) at high temperatures.…”

Plastic deformation of CoO single crystals

“…The kinetics of processes (i) and (iii) is controlled by vacancy migration ; the chemical diffusion coefficient D can be computed from [28]. We obtain a value D = 2.6 x 10-6 cm'/s at 1200 °C and JlJt = [18].…”

Parabolic Growth of Nonuniformly Doped Oxides Containing Aliovalent Impurities on Dilute Alloys

“…This oxide is chosen again as an example of a compound having a relatively complex defect structure since, even neglecting the presence of minority defects in the oxygen sublattice, it contains different kinds of vacancies and possibly also metal interstitials (20)(21)(22). The situation is examined for both the presence and absence of metal interstitials to determine the difference that this produces on the effect of the impurities.…”