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Understanding the behaviour of the room-temperature molecular ferroelectric 5,6-dichloro-2-methylbenzimidazole using symmetry adapted distortion mode analysis

DOI: 10.1021/jacs.8b08591 DOI Help

Authors: Huiyu Liu (Durham University) , Weiguo Zhang (University of Houston) , P. Shiv Halasyamani (University of Houston) , Harold T. Stokes (Brigham Young University) , Branton J. Campbell (Brigham Young University) , John S. O. Evans (Durham University) , Ivana Radosavljevic Evans (Durham University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: September 2018

Abstract: The exploitable properties of many functional materials are intimately linked with symmetry-changing phase transitions. These include properties such as ferroelectricity, second harmonic generation, conductivity, magnetism and many others. We describe a new symmetry-inspired method for systematic and exhaustive evaluation of the symmetry changes possible in molecular systems using molecular distortion modes and how different models can be automatically tested against diffraction data. The method produces a quantitative structural landscape from which the most appropriate structural description of a child phase can be chosen. It can be applied to any molecular of molecular-fragment containing material where a (semi) rigid molecule description is appropriate. We exemplify the method on 5,6-dichloro-2-methylbenzimidazole (DC-MBI), an important molecular ferroelectric. We show that DC-MBI under-goes an unusual symmetry-lowering transition on warming from orthorhombic Pca21 (T ≲ 400 K) to monoclinic Pc. Contrary to expectations, the high temperature phase of DC-MBI remains polar.

Subject Areas: Materials, Chemistry

Instruments: I11-High Resolution Powder Diffraction