Reinvestigation of the Phase Transition in ABW-Type CsLiSO4: Symmetry Analysis and Atomic Distortions
✍ Scribed by V Kahlenberg
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 293 KB
- Volume
- 138
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
ABW-type CsLiSO 4 shows a reversible structural phase transition at approximately 202 K. The transformation is translationengleich and the space group symmetries of the two different polymorphic forms are Pnma (phase I) and P 2 n 11 (phase II), respectively. The transition was reinvestigated using a group theoretical approach based on the published structural data of the two modifications. A combined rotation of the SO 4 and LiO 4tetrahedra was taken as the primary order parameter inducing the transformation. Projection operator calculations revealed that the transition can be associated with the irreducible representation ؉ 3 of Pnma. Displacements of the Li, S, and Cs ions as well as the occurrence of certain strain components are symmetry allowed, too, and can couple to . The global tilting pattern is compared with the rotational distortions observed in the transitions of ABW-type CsZnPO 4 . A rigid-unit mode approach is proposed for the explanation of the transitions.