Oxygen nonstoichiometry and chemical stability of Nd2−xSrxNiO4+δ

Nonstoichiometric variation of oxygen content in Nd2−xSrxNiO4+δ (x=0, 0.2, 0.4) and decomposition P(O2) were determined by means of high temperature gravimetry and coulometric titration. The measurements were carried out in the temperature range from 873 to 1173 K and the P(O2) range from 10−20 to 1 bar. Nd2−xSrxNiO4+δ shows the oxygen excess and the oxygen deficient composition depending on P(O2), temperature, and the Sr content. To evaluate the characteristics of oxygen nonstoichiometric behavior, partial molar enthalpy of oxygen was calculated. The value of partial molar enthalpy of oxygen slightly approaches zero as δ increases in the oxygen excess region while that is independent of δ in the oxygen deficient region. Discussion was made by comparing data of this study with nonstoichiometric and thermodynamic data of La2−xSrxNiO4+δ: Nd2−xSrxNiO4+δ show more oxygen excess than La2−xSrxNiO4+δ in the higher P(O2) region, while the nonstoichiometric behavior in the oxygen deficient composition is almost the same. The variation of partial molar enthalpy of oxygen with δ for Nd2−xSrxNiO4+δ in the oxygen excess region is much smaller than that of La2−xSrxNiO4+δ. The oxygen nonstoichiometric behavior of Nd2−xSrxNiO4+δ is more ideal-solution-like than that of La2−xSrxNiO4+δ.