Incommensurately Modulated Structure of K₂SeO₄

Abstract

The modulated structure in the incommensurate phase of K₂SeO₄ has been analyzed at 113 K by X-ray diffractometry based on the concept of four-dimensional space. The final R-factor was 0.046 for all 905 reflections and 0.087 for 326 satellite reflections.
The modulation is characterized by the rotation of SeO₄ groups around b-direction and the associated translation of K atoms along c-axis. The eigenvector of the modulation mode was determined from the observed atomic displacement pattern and it is compared with that of Σ₂ soft mode determined by neutron experiment.