Acta Crystallographica Section B

Structural Science

Volume 55, Part 6 (December 1999)

research papers

Acta Cryst. (1999). B55, 853-866 [ doi:10.1107/S0108768199005479 ]

Symmetry classification of the layered perovskite-derived A_nB_nX_3n+2 structures

I. Levin and L. A. Bendersky

Abstract: The effects of combinations of octahedral tilts on the symmetries of layered A_nB_nX_3n+2 structures were considered. Two complementary approaches were used to deduce the symmetries. The space groups associated with different tilt systems were determined for structures with different layer thicknesses (n values) and for structures with different layer stacking arrangements. For the most symmetrical tilts about the orthorhombic axes of the A_nB_nX_3n+2 structure, maximal group/subgroup relations were established. Comparison of these results with experimental data available in the literature suggests that the symmetries of most observed A_nB_nX_3n+2 compounds are fully determined by the tilt systems adopted by rigid BX₆ octahedra. The most common tilt system observed at room temperature is a combination of an in-phase tilt about an orthorhombic axis parallel to the pseudo-fourfold axis of the octahedron with a tilt about an orthorhombic axis perpendicular to the layers.

Keywords: Symmetry; Perovskites; Layered structures.