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

Journal article

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.

Authors: Boström, H; Hill, J; Goodwin, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Royal Society of Chemistry
• Journal: Physical Chemistry Chemical Physics
• Volume: 18
• Pages: 31881-31894
• Publication date: 2016-10-01
• Acceptance date: 2016-10-20
• DOI: 10.1039/c6cp05730f
• ISSN: 1463-9084