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Figure 1
(a) Relationship between the phases generated from the I4/mmm aristotype through combinations of the [{\rm X}_{2}^{+}], [{\rm X}_{1}^{-}] and [{\rm X}_{3}^{-}] irreps. (b) Rotation and tilting of SnO6 octahedra, highlighting the hybrid improper coupling of the octahedral distortions, [{\rm X}_{2}^{+}] and [{\rm X}_{3}^{-}] to the polar mode, Γ[{}_{5}^{-}] in A21am, and, similarly, the trilinear coupling between [{\rm X}_{3}^{-}], [{\rm X}_{1}^{-}] and the antiferroelectric mode, [{\rm M}_{5}^{+}] in Pnab. (c) Crystal structures of the phases of Sr3Sn2O7 that have been experimentally observed by temperature (Yoshida et al., 2018BB1) and pressure, showing the different order parameter directions. Sr displacements are indicated by blue and red arrows with crosses indicating no displacement. This results in an antiferroelectric distortion ([{\rm M}_{5}^{+}]) for Pnab and a polar distortion (Γ[{}_{5}^{-}]) for A21am.

Journal logo STRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
Volume 81| Part 3| June 2025| Pages 318-324
https://doi.org/10.1107/S2052520625002306
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