The influence of chromium on the defect structure and their mobility in nonstoichiometric cobaltous oxide

Abstract

Defect structure and the mobility of point defects in pure metal deficient cobalt oxide (Co 1− y O) and in Co 1− y O–Cr 2O 3 solid solutions have been studied as a function of temperature (1223–1573 K) and oxygen pressure (10–10 5 Pa) using microthermogravimetric techniques. It has been shown that the predominant defects in pure and Cr-doped cobaltous oxide are singly ionized cation vacancies, and 3% at of dopant is high enough to fix the concentration of predominant defects in such solid solutions on a constant level being much higher than in pure Co 1− y O. Re-equilibration rate measurements have demonstrated that the chemical diffusion coefficient and thereby the mobility of point defects in pure Co 1− y O is concentration independent, strongly suggesting that in spite of rather high their concentration no interactions and clustering of defects is to be expected. On the other hand, in Cr-doped cobaltous oxide, re-equilibration rate measurements have shown, that in this case the defect structure is more complicated, although singly ionized cation vacancies seem to be still predominant defects.