Defect chemical and statistical thermodynamic studies on oxygen nonstoichiometric Nd2 − xSrxNiO4 + δ

In order to elucidate how oxygen content changes in Nd_2 − xSr_xNiO_4 + δ (x = 0, 0.2, 0.4), defect chemical and statistical thermodynamic analyses were carried out. The relationship among δ, P(O₂), and T were analyzed by a defect equilibrium model. Since Nd_2 − xSr_xNiO_4 + δ shows metal like band conduction at high temperatures, chemical potential of hole is expressed by the integration of the Fermi-Dirac distribution function and the density of state. The nonstoichiometric variation of oxygen content in Nd_2 − xSr_xNiO_4 + δ can be explained by the defect equilibrium model with a regular solution approximation. Partial molar entropy and partial molar enthalpy of oxygen are calculated from the nonstoichiometric data and Gibbs–Helmholtz equation. The relationship among defect structure, defect equilibrium, and thermodynamic quantities is elucidated by the statistical thermodynamic model. Thermodynamic quantities are calculated by the statistical thermodynamic model with the results of defect chemical analysis and compared with those obtained from experimental results. Thermodynamic quantities calculated by the statistical thermodynamic model can explain rough tendency of those obtained from the δ–T–P(O₂) relationship.