Controlling multiple orderings in metal thiocyanate molecular perovskites Ax{Ni[Bi(SCN)6]} |
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| Authors: | Jie Yie Lee Sanliang Ling Stephen P Argent Mark S Senn Laura Caadillas-Delgado Matthew J Cliffe |
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| Institution: | School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD UK.; Advanced Materials Research Group, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD UK ; Department of Chemistry, University of Warwick, Gibbet Hill, Coventry CV4 7AL UK ; Institut Laue Langevin, 71 Avenue des Martyrs – CS 20156, 38042 Grenoble France |
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| Abstract: | We report four new A-site vacancy ordered thiocyanate double double perovskites, , A = K+, NH4+, CH3(NH3)+ (MeNH3+) and C(NH2)3+ (Gua+), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders suggest a new route to non-centrosymmetric perovskites, and mean this family of materials could contain excellent candidates for piezo- and ferroelectric applications.Metal thiocyanate hybrid perovskites can have multiple simultaneous complex orderings and combining these orderings appropriately can produce non-centrosymmetric structures. |
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