Defect Structure and Oxide-ion Conduction in (La, Sr)2NiO4+δ with Layered Perovskite Structure

Atomic configuration of La2-xSrxNiO4+delta (x = 1/4) with a layered perovskite structure was investigated by a molecular dynamics simulation and a reverse Monte Carlo modelling using a Faber-Ziman structure factor in addition to a Bragg profile. It is confirmed that the Sr-substituted material conducts interstitial oxide ions through the rock-salt layer as in the case of La2NiO4+delta, and thus it is supposed that the conduction mechanism is not influenced significantly by the Sr substitution. However, a difference between local structures around La and Sr demonstrates that the interstitial oxide ions exist around not Sr but La, and this tendency can be considered to be due to electrostatic interaction among the cations and the oxide ions. Such a structural feature may be one of the reasons for inferior oxide-ion diffusion in the Sr-substituted material.