Insights into oxygen migration in LaBaCo2O6-delta perovskites from in situ neutron powder diffraction and bond valence site energy calculations

Funding: The EPSRC CRITICAT Centre for Doctoral Training (EP/ L016419/1) for a studentship for F.H. STFC for provision of beamtime at the ISIS Neutron and Muon Source (award RB1910262).Layered cobalt oxide perovskites are important mixed ionic and electronic conductors. Here, we investigate LaBaCo2O6−δ 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 near-identical oxygen cycling capacities. Migration barriers for oxide ion conduction calculated using the bond valence site energy approach vary from Eb ∼ 2.8 eV for the cubic perovskite to Eb ∼ 1.5 eV for 2D transport in the layered system. Vacancy-ordered superstructures were observed at low temperatures, 350–400 °C for δ = 0.25 and δ = 0.5. The vacancy ordering at δ = 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 Eb = 0.5 eV and 3D channels with Eb = 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 LnBaCo2O6−δ perovskites with reduced symmetry.Publisher PDFPeer reviewe