High-resolution electron microscopy of the incommensurate structure in Sr₂Nb₂O₂

The incommensurate structure of strontium diniobate, Sr₂Nb₂O₇, is formed below 488 K with a one-dimensional lattice modulation along the [100] direction. A model of the atom displacements due to this lattice modulation has been proposed from an analysis of the systematic extinction of the extra reflections due to the incommensurate structure. High-resolution electron microscopy clearly reveals the lattice modulation in the incommensurate phase. The observed images are well interpreted by image simulation of the proposed model.