Characterisation of La2NiO4+δ using in-situ high temperature neutron powder diffraction

La2NiO4+delta, has been studied using in-situ high temperature neutron diffraction over a temperature range of 25-800 degreesC in vacuum. The behaviour of this material, and in particular the oxygen interstitial content, is discussed and quite remarkable bond length changes observed. It is observed that at temperatures above 150 degreesC La2NiO4+delta transforms to the tetragonal I4/mmm structure and maintains this over the entire temperature range on both heating and cooling. The loss of the interstitial oxygen was observed over the low temperature region of the study and significant changes in both lattice constant and bond lengths found to mirror these changes, indicating the structural importance of the interstitial oxygen. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.