Modulated structure of La2NiO4+delta as a mechanism of oxygen excess accommodation

A microstructural characterization by means of high resolution transmission electron microscopy has been performed in La2NiO4+delta in order to confirm the distribution of the oxygen excess. A structure commensurately modulated along [010] with modulation period a(s) = 3a, and another with b(s) = 4b along [100] were found. The origin of such modulations is discussed in terms of the irregular distribution of interstitial oxygen atoms within the crystal lattice. Although the structural changes may be electron beam induced and these new phases are minorities and possibly metastable, the results contribute new information about how the interstitial oxygen can be accommodated. (C) 1996 Academic Press, Inc.