Gravimetric Determination of Defect Concentrations in NiO

Thermogravimetric measurements were made on NiO from 800° to 1100°C over the oxygen pressure range 10 −1 to 10 −4 atm. On the basis of complementary conductivity measurements showing a P (O 2 ) 1/5 oxygen pressure dependence, it is proposed that the predominant defects are described by an electroneutrality condition involving doubly ionized metal vacancies, impurities, and electron holes, 2[ V” M ]=[ F M ]+ p. It is shown that for this defect model, the weight change relative to a low oxygen pressure reference weight is a measure of the effective vacancy concentration, defined as [ V” M ] eff ≡[ V” M ]‐≡[ F M ], and therefore has the same oxygen pressure dependence as the electron hole concentration followed in the conductivity measurements. The expression [ V” M ] eff =0.168 P (O 2 ) 1/5 exp (−0.86±0.15/ kT ) is derived to express the effective vacancy concentration in NiO. The probable effective impurity content of the specimens used is calculated.