Irreversible electron-induced structural change during HREM imaging in lithium Ruddlesden-Popper phases in the series Li2Lax(Nb2n-3xTi3x-n)O3n+1 (n = 2, 3, 4) and Li2Sr1.5(Nb3-xFex)O10-x

Several lithium Ruddlesden-Popper compounds are investigated by TEM (ED and HREM) in the series Li2Lax(Nb2n-3xTi3x-n) O3n+1 (n = 2, 3, and 4, for x = 0.833, 1.78, and 2.25, respectively) and Li2Sr1.5(Nb3-xFex) O10-x (for n = 3; x = 0 and 0.115). These studies confirm the crystal structures previously established from single crystal X-ray diffraction data: they consist of perovskite layers separated by Li+ ions in distorted tetrahedral coordination. After the HREM study, for all the examined compounds, an irreversible structural change is evidenced leading to a unique model (space group I4/mmm) characterized by the preservation of the perovskite layers and by a substantial shrinking of the c parameter (perpendicular to the perovskite slabs). In the hypothesis of the conservation of the cells contents, this phenomenon is explained by a concomitant change in the Li+ coordination which becomes octahedral. (C) 1999 Acndemic Press.