Using the tools of group theory we have mapped out the symmetry consequences of structural distortions in hybrid layered perovskites. These distortions include octahedral tilting and cation ordering within the inorganic layers as well as orientational ordering of organic cations in the organic layers. This analysis is coupled with synthesis and crystal structure determination of a wide variety of A2MX4 (A = protonated amine; M = Mn, Cu, Pb, Cd; X = Cl, Br, I) hybrid layered n = 1 Ruddlesden-Popper phases and analogous A4MM'X8 (M = Ag, Cu, Na; M' = Bi, Sb, In; X = Cl, Br, I) double perovskite phases. The combined analysis shows that certain modes of octahedral tilting are strongly favored, and those modes control the orientational ordering of the protonated amines. This information is used to guide our search for new lead-free ferroelectrics and multiferroics among this large class of compounds.

Assessing the symmetries of phase transitions in hybrid layered halide perovskites – The search for new ferroelectrics and multiferroics

ACS Spring Meeting 2021

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