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)O10x

摘要

Several Li 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, respp. ) 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 XRD 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 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. 40 refs.