Structural observations on La2(Ni,Co)O4±δ phases determined from in situ neutron powder diffraction

In situ neutron powder diffraction data have been analysed for a number of compositions in the solid solution series La2Ni1-x Co x O4±δ over the temperature range 150-650 deg. C. High-quality Rietveld refinements indicate no major structural transitions have occurred in any of the compositions, although close examination of the Ni/Co-O bond distances highlight changes in the coordination environment with increasing temperature. Further, the changes in the coordination can be correlated to changes in both the oxide ion and electronic conductivity indicating a direct link between transport properties, bonding and transition metal valence state in these Co containing layered perovskites. - Graphical abstract: Two phase fit for La2CoO4+δ recorded at 150 deg. C showing the peak splitting of the two orthorhombic phases. Both phases transform to the tetragonal modification at elevated temperatures