Structural deformation and non-stoichiometry of La4Co3O10+δ

The structural deformation and the incorporation of an excess of oxygen in La4Co3O10 + delta have been investigated for the compositions delta = 0.00 and delta = 0.30. Rietveld analysis of high-resolution powder neutron diffraction data reveals symmetry lowering due to the displacement of oxygen atoms from the ideal positions of the Ruddlesden-Popper type structure, space group P2(1)/a. The resulting rotations of the CoO6 octahedra within the triple perovskite layers are similar to that commonly found in perovskites. However, the octahedra at the interface towards the LaO layers are less tilted, but more distorted than the central octahedra of the triple perovskite layers. The additional 0.30 oxygen atom of La4Co3O10.30 is distributed on interstitial, tetrahedral sites within the LaO layers (ideal coordinates 1/4,1/4,3/4). Bond valence sum calculations show that the symmetry reduction, the structural distortions and the incorporation of additional oxygen result in relief of structural strain of La4Co3O10 + delta. The strain is probably caused by size mismatch between the LaO and CoO structural fragments.