Structural analysis of La2-xSrxNiO4 + δ by high temperature X-ray diffraction

High temperature X-ray diffraction measurements were made on oxygen nonstoichiometric La2-xSrxNiO4 + delta in N-2-O-2 atmosphere at 873-1173 K. Crystal structure of La2-xSrxNiO4 + delta at high temperatures was analyzed using the tetragonal symmetry, I4/mmm. As the amount of excess oxygen increases, the lattice parameter perpendicular to the perovskite and the rock salt layers increases and that parallel to the layers decreases. As a consequence, the cell volume is almost constant regardless of the oxygen content variation. The lattice parameters essentially depend on temperature and delta. The relationship among the lattice parameters, temperature, and delta is expressed by the total differential form of the lattice parameters. The model with linear approximation can well explain the variation of the lattice parameters with delta and temperature. Apparent and true thermal expansion coefficients were calculated from the variation of the lattice parameters with temperature. Crystal structure of La2-xSrxNiO4 (+) (delta) was estimated by the Rietveld analysis. It is elucidated that the space in the rock salt layer decreases as the acceptor concentration (x + 2 delta) increases. The variation of the space in the rock salt layer is consistent with the oxygen nonstoichiometric behavior that the interstitial oxygen formation is suppressed as x and delta increase. (C) 2010 Elsevier B.V. All rights reserved.