Ferroelectrics, featuring polar structures that are switchable under an external field,have been widely used in diverse technological applications. As the intermediary state between paraelectric and ferroelectric phases, the incommensurate (IC) behaviors are of great significance for the understanding on polarization switching, as well as the underlying chemistry and physics of aperiodic materials.
In the study published in J. Am. Chem. Soc., the research group led by Prof. LUO Junhua from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Science (CAS) reported unusual incommensurately modulated structures in an organic molecular ferroelectric.
Distinct IC states are clearly expatiated during its structural phase transitions, and the incommensurately modulated lattice is ~7 times as large as its periodic prototype. At 150 K, the IC crystal structure is refined using a (3+1)D superspace group of Pbca(00g)0s0. The satellite reflections are indexed with four integers as H = ha*+ kb*+ lc* +mq with the modulated vector of q = (0, 0, 0.1589).
As decreases to 148 K, its superspace group was determined as Pb21a(00g)s00 with the indices of H = ha*+kb*+lc*+mq (q = 0.143); its polar characteristics should be reminiscent of ferroelectricity. To our best knowledge, this long-range ordering IC structural modulation based on organic ferroelectric is proposed for the first time.
Further studies disclose that slowing down of dynamic motions of anionic moieties dominates its modulation behaviors and the ferroelectric polarization (~0.65 μC/cm2). The combination of unique IC structural modulations and ferroelectricity in this organic crystal is of significance for the assembly of an artificially modulated lattice. From the structure viewpoint, it is a great opportunity to explore the incommensurately modulated architectures in the pure organic ferroelectric systems.
This work is supported by NSFC, the NSF of Fujian Province, the Strategic Priority Research Program of the Chinese Academy of Sciences, the Youth Innovation Promotion of CAS and State Key Laboratory of Luminescence and Applications.
Long-range ordering incommensurate structural modulations in organic molecular ferroelectric (Image by Prof. LUO's Group)
Contact:
Prof. LUO Junhua
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
Email: jhluo@fjirsm.ac.cn
