Issue 46, 2016

Columnar shifts as symmetry-breaking degrees of freedom in molecular perovskites

Abstract

We introduce columnar shifts—collective rigid-body translations—as a structural degree of freedom relevant to the phase behaviour of molecular perovskites ABX3 (X = molecular anion). Like the well-known octahedral tilts of conventional perovskites, shifts also preserve the octahedral coordination geometry of the B-site cation in molecular perovskites, and so are predisposed to influencing the low-energy dynamics and displacive phase transitions of these topical systems. We present a qualitative overview of the interplay between shift activation and crystal symmetry breaking, and introduce a generalised terminology to allow characterisation of simple shift distortions, drawing analogy to the “Glazer notation” for octahedral tilts. We apply our approach to the interpretation of a representative selection of azide and formate perovskite structures, and discuss the implications for functional exploitation of shift degrees of freedom in negative thermal expansion materials and hybrid ferroelectrics.

Graphical abstract: Columnar shifts as symmetry-breaking degrees of freedom in molecular perovskites

Article information

Article type
Paper
Submitted
18 ส.ค. 2559
Accepted
20 ต.ค. 2559
First published
20 ต.ค. 2559
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2016,18, 31881-31894

Columnar shifts as symmetry-breaking degrees of freedom in molecular perovskites

H. L. B. Boström, J. A. Hill and A. L. Goodwin, Phys. Chem. Chem. Phys., 2016, 18, 31881 DOI: 10.1039/C6CP05730F

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