Phase related oxygen permeation through Sr-doped LaCoO3-δ

Oxygen permeation results through La1-xSrxCoO3-δ are reported. It is shown that in the temperature region 750 - 775 °C an order-disorder of the oxygen sublattice occurs. The low temperature ordered phase is studied by X-Ray powder diffraction (XRD), neutron diffraction as well as selected area electron diffraction (SAED) together with High Resolution Transmission Electron Microscopy (HRTEM) coupled with Parallel Electron Energy Loss Spectroscopy (PEELS) and Energy Dispersive X-Ray spectroscopy (EDX). Although the long range methods XRD and neutron diffraction showed no indications for an oxygen vacancy ordering, SAED and HRTEM showed micro domains exhibiting an ac x ac x 2ac superstructure, along with regions without indications for a superstructure. The superstructure could be interpreted in terms of an oxygen vacancy ordering due to which a large part of the oxygen vacancies were trapped in regions with the superstructure and so effectively reducing the ionic conductivity. By means of PEELS it was shown that the cobalt ions within the superstructure regions have a higher oxidation state than the cobalt ions in the non-ordered regions