A Detailed Structural Analysis of Cd_xNb₆(O,F)₁₆

Abstract

The structure of CdxNb6(O,F)16 was re‐determined from X‐ray single crystal diffraction data. It crystallizes in the orthorhombic LiNb6O15F structure type in the space group Pmma. Remarkably, there is a shift of the Nb positions along the short b axis out of the mirror plane and a partial and disordered occupancy of square channels by Cd. The composition was refined to Cd0.274(6)Nb6O14.55F1.45. Light microscopy and scanning electron microscopy (SEM) images show the frequent intergrowth of crystallites on the micrometer scale whereas high‐resolution transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) images reveal a perfectly ordered structure in most areas investigated. A single grain boundary was uncovered with the structures in the adjacent domains tilted by 4° in respect of each other. In parts of the interface, the adjacent domains are coherently connected in a way not observed before. Additional defects are present at irregular intervals that apparently compensate resulting strain.