Abstract

The structural deformation and the incorporation of an excess of oxygen in La₄Co₃O_{10 + δ} have been investigated for the compositions δ = 0.00 and δ = 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 P2₁/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 La₄Co₃O_10.30 is distributed on interstitial, tetrahedral sites within the LaO layers (ideal coordinates ¼,¼,¾). 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 La₄Co₃O_{10 + δ}. The strain is probably caused by size mismatch between the LaO and CoO structural fragments.