Insights into Oxygen Migration in LaBaCo2O6-δ Perovskites from In Situ Neutron Powder Diffraction and Bond Valence Site Energy Calculations

Layered cobalt oxide perovskites are important mixed ionic and electronic conductors. Here, we investigate LaBaCo2O6-delta using in situ neutron powder diffraction. This composition is unique because it can be prepared in cubic, layered, and vacancy-ordered forms. Thermogravimetric analysis and diffraction reveal that layered and disordered samples have nearidentical oxygen cycling capacities. Migration barriers for oxide ion conduction calculated using the bond valence site energy approach vary from E-b similar to 2.8 eV for the cubic perovskite to E-b similar to 1.5 eV for 2D transport in the layered system. Vacancy-ordered superstructures were observed at low temperatures, 350-400 degrees C for delta = 0.25 and delta = 0.5. The vacancy ordering at delta = 0.5 is different from the widely reported structure and involves oxygen sites in both CoO2 and LaO planes. Vacancy ordering leads to the emergence of additional migration pathways with low-energy barriers, for example, 1D channels with E-b = 0.5 eV and 3D channels with E-b = 2.2 eV. The emergence of these channels is caused by the strong orthorhombic distortion of the crystal structure. These results demonstrate that there is potential scope to manipulate ionic transport in vacancy-ordered LnBaCo(2)O(6-delta) perovskites with reduced symmetry.