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 π-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 crystals1. Croconic acid, an ingredient of black dyes2, was recently found to have a hydrogen-bonded polar structure in a crystalline state3. 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 π-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this molecular crystal exhibits the highest spontaneous polarization (∼20 μC 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.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Sugawara, T. & Takasu, I. Tautomerism in the solid state. Adv. Phys. Org. Chem. 32, 219–265 (1999)
Keil, D., Hartmann, H. & Reichardt, C. Synthesis and spectroscopic characterization of new NIR absorbing (2-thienyl) and (4-dialkylaminoaryl)-substituted croconic acid dyes. Liebigs Ann. Chem. 1993, 935–939 (1993)
Braga, D., Maini, L. & Grepioni, F. Crystallization from hydrochloric acid affords the solid-state structure of croconic acid (175 years after its discovery) and a novel hydrogen-bonded network. CrystEngComm 6, 1–3 (2001)
Seitz, G. & Imming, P. Oxocarbons and pseudooxocarbons. Chem. Rev. 92, 1227–1260 (1992)
Semmingsen, D. & Groth, P. Deltic acid, a novel compound. J. Am. Chem. Soc. 109, 7238–7239 (1987)
Semmingsen, D., Hollander, F. J. & Koetzle, T. F. A neutron diffraction study of squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione). J. Chem. Phys. 66, 4405–4412 (1977)
Braga, D., Cojazzi, G., Maini, L. & Grepioni, F. Reversible solid-state interconversion of rhodizonic acid H2C6O6 into H6C6O8 and the solid-state structure of the rhodizonate dianion C6O6 2- (aromatic or non-aromatic?). N. J. Chem. 25, 1221–1223 (2001)
Feder, J. Two-dimensional ferroelectricity. Ferroelectrics 12, 71–84 (1976)
Katrusiak, A. & Szafrański, M. Ferroelectricity in NH···N hydrogen bonded crystals. Phys. Rev. Lett. 82, 576–579 (1999)
Horiuchi, S. & Tokura, Y. Organic ferroelectrics. Nature Mater. 7, 357–366 (2008)
Zikmund, Z. et al. Search for new molecular organic ferroelectrics. Ferroelectrics 58, 223–228 (1994)
Washino, M., Yamada, K. & Kurita, Y. The dipole moments and molecular structures of croconic acid and dimethyl croconate. Bull. Chem. Soc. Jpn 31, 552–555 (1958)
King-Smith, R. D. & Vanderbilt, D. Theory of polarization of crystalline solids. Phys. Rev. B 47, 1651–1654 (1993)
Hellwege, K.-H. & Hellwege, A. M. (eds) Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology. New Series, Group III: Crystal and Solid State Physics Vol. 16a, Ferroelectric and Related Substances: Oxides 66–77 (Springer, 1981)
Fiebig, M., Fröhlich, D., Lottermoser & Maat, M. Probing of ferroelectric surface and bulk domains in RMnO3 (R = Y, Ho) by second harmonic generation. Phys. Rev. B 66, 144102 (2002)
Fukunaga, M. & Noda, Y. New technique for measuring ferroelectric and antiferroelectric hysteresis loops. J. Phys. Soc. Jpn 77, 064706 (2008)
Noda, K. et al. Remanent polarization of evaporated films of vinylidene fluoride oligomers. J. Appl. Phys. 93, 2866–2870 (2003)
Tajitsu, Y., Ogura, H., Chiba, A. & Furukawa, T. Investigation of switching characteristics of vinylidene fluoride/trifluoroethylene copolymers in relation to their structures. Jpn. J. Appl. Phys. 26, 554–560 (1987)
Kroupa, J., Vanẽk, P., Krupkova, R. & Zikmund, Z. Dielectric and optical properties of weak ferroelectric cyclohexan-1,1’-diacetic acid. Ferroelectrics 202, 229–234 (1997)
Kamishima, Y., Akishige, Y. & Hashimoto, M. Ferroelectricity activity on organic crystal trichloroacetamide. J. Phys. Soc. Jpn 60, 2147–2150 (1991)
Gilli, G., Bellucci, F., Ferretti, V. & Bertolasi, V. Evidence for resonance-assisted hydrogen bonding from crystal-structure correlations on the enol form of the β-diketone fragment, V. J. Am. Chem. Soc. 111, 1023–1028 (1989)
Ling, Q.-D. et al. Polymer electronic memories: materials, devices and mechanisms. Prog. Polym. Sci. 33, 917–978 (2008)
Dalton, L. R. et al. Synthesis and processing of improved organic second-order nonlinear optical materials for applications in photonics. Chem. Mater. 7, 1060–1081 (1995)
Kresse, G. & Furthmueller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996)
Schmidt, M. W. et al. General atomic and molecular electronic structure system. J. Comput. Chem. 14, 1347–1363 (1993)
Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999)
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996)
Heyd, J., Scuseria, G. E. & Ernzerhof, M. Hybrid functionals based on a screened Coulomb potential. J. Chem. Phys. 118, 8207–8215 (2003)
Dion, M., Rydberg, H., Schröder, E., Langreth, D. C. & Lundqvist, B. I. Van der Waals density functional for general geometries. Phys. Rev. Lett. 92, 246401 (2004)
Lazić, P. et al. JuNoLo — Jülich nonlocal code for parallel post-processing evaluation of vdW-DF correlation energy. Comput. Phys. Commun. 181, 371–379 (2010)
S.H. is grateful for support by a Grant-in-Aid for Scientific Research (No. 20110003) by the Ministry of Education, Culture, Sports, Science and Technology of Japan. The research leading to the theoretical results received funding from the European Research Council under the European Community, 7th Framework Programme - FP7 (2007-2013)/ERC Grant Agreement n. 203523.
Author Contributions S.H. did the sample preparation and the dielectric measurements, and wrote most of the paper, Y. Tokunaga optimized the P-E hysteresis data and made the pyroelectric and resistivity measurements, G.G. and S.P. did the calculations and wrote a significant part of the discussion, H.I. and R.S. performed the second harmonic generation imaging microscopy and wrote the paper, R.K. contributed to the diffraction studies, and Y. Tokura contributed to the design of the studies and writing of the paper.
The authors declare no competing financial interests.
About this article
Cite this article
Horiuchi, S., Tokunaga, Y., Giovannetti, G. et al. Above-room-temperature ferroelectricity in a single-component molecular crystal. Nature 463, 789–792 (2010). https://doi.org/10.1038/nature08731
Nature Communications (2021)
Nature Communications (2021)
Optical and structural properties of aluminium nitride thin-films synthesized by DC-magnetron sputtering technique at different sputtering pressures
Microsystem Technologies (2021)
Nanotechnology for Environmental Engineering (2021)
Nature Communications (2019)