Abstract
Nonstoichiometric variation of oxygen content in La 2 − x Sr x NiO 4 + δ ( x = 0, 0.1, 0.2, 0.3, 0.4) and decomposition P(O 2) were determined by means of high temperature gravimetry and coulometric titration. The measurements were carried out in the temperature range between 873 and 1173 K and the P(O 2) range between 10 − 20 and 1 bar. La 2 − x Sr x NiO 4 + δ showed the oxygen excess and the oxygen deficient compositions depending on P(O 2), temperature, and the Sr content. The value of partial molar enthalpy of oxygen approaches zero as δ increases in the oxygen excess region, which indicate that the interstitial oxygen formation reaction is suppressed as δ increase. The relationship between δ and log P(O 2) were analyzed by two types of defect equilibrium models. One is a localized electron model, and the other is a delocalized electron model. Both models can well explain the oxygen nonstoichiometry of La 2 − x Sr x NiO 4 + δ with a regular solution approximation.
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