Above-room-temperature ferroelectricity in a single-component molecular crystal

Abstract

Ferroelectrics are electro-active materials that can store and switch their polarity (ferroelectricity), sense temperature changes (pyroelectricity), interchange electric and mechanical functions (piezoelectricity), and manipulate light (through optical nonlinearities and the electro-optic effect): all of these functions have practical applications. Topological switching of pi-conjugation in organic molecules, such as the keto-enol transformation, has long been anticipated as a means of realizing these phenomena in molecular assemblies and crystals. Croconic acid, an ingredient of black dyes, was recently found to have a hydrogen-bonded polar structure in a crystalline state. Here we demonstrate that application of an electric field can coherently align the molecular polarities in crystalline croconic acid, as indicated by an increase of optical second harmonic generation, and produce a well-defined polarization hysteresis at room temperature. To make this simple pentagonal molecule ferroelectric, we switched the pi-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this molecular crystal exhibits the highest spontaneous polarization ( approximately 20 muC cm(-2)) in spite of its small molecular size, which is in accord with first-principles electronic-structure calculations. Such high polarization, which persists up to 400 K, may find application in active capacitor and nonlinear optics elements in future organic electronics.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…In some cases, the electromechanical activity was observed in symmetry-forbidden cases such as tobacco mosaic virus 148 and attributed to flexoelectric coupling. 149 Finally, several molecular crystals including glycine, 150 croconic acid, 151,152 etc. were found to display ferroelectricity, providing new insights into the structure and properties of these materials and potentially leading to new applications.…”

Simulation and understanding of atomic and molecular quantum crystals

“…This correlation consists of H atoms in neighboring H-bonds being strongly coupled due to the energetic requirement for satisfying the "ice rules" (Singer et al, 2005); in the KDP and H2SQ systems this condition implies that each molecule participates in 4 different H-bonds, two of which have donating character and the rest accepting. H-bond ferroelectric materials currently are attracting a lot of attention because polar order near room-temperature has been revealed in some organic species (Horiuchi et al, 2005;Horiuchi et al, 2010). This finding opens the possibility for manufacturing cheaper and more environment friendly nanoelectronic components and devices.…”

Fabrication of diisopropylammonium bromide aligned microcrystals with in-plane uniaxial polarization

“…Molecular ferroelectrics, on the other hand, readily grow into large single crystals and afford greater synthetic flexibility than polymers, while avoiding many of the difficulties presented by oxides. For these and other reasons, there has been renewed interest in the development of new high-performance molecular ferroelectrics [12][13][14][31][32][33][34][35]. Some of the key properties of useful ferroelectrics are high spontaneous polarization, a transition temperature well above room temperature, and a low coercive field [7].…”