Mar 10 2010
Sachio Horiuchi of Correlated Materials Photoelectronics Group, the Photonics Research Institute of the National Institute of Advanced Industrial Science and Technology (AIST); Yoshinori Tokura of the Department of Applied Physics, Graduate School of Engineering and Ryo Shimano of the Department of Physics, Graduate School of Science, both of the University of Tokyo; and Yusuke Tokunaga and Hiroki Itou of the Japan Science and Technology Agency (JST) have jointly discovered that croconic acid exhibits ferroelectricity and the largest polarization at room temperature among low-molecular-weight organic compounds. This study is a part of the "Tokura Multiferroics Project" of the Exploratory Research for Advanced Technology (ERATO) of JST.
Ferroelectrics are important materials and are used to perform various functions in the fields of both electronics and photonics; they are used in memory, capacitors, piezoelectric devices, and optical devices. The development of high-performance organic ferroelectrics is expected to encourage new applications utilizing the characteristics of organic compounds. However, the progress of organic ferroelectrics, particularly those made of small molecules, has been slow because very few organic ferroelectrics are known so far and they have low operating-temperatures and weak polarization properties.
Croconic acid has a simple molecular structure and contains carbon, hydrogen, and oxygen atoms (Fig. 1). We found that croconic acid is an excellent organic ferroelectric, and its spontaneous polarization is close to that of barium titanate, one of representative ferroelectric ceramics. In addition, the electric field required to reverse the polarity of croconic acid is significantly weaker compared to that required in the case of typical ferroelectrics made of organic polymers. The ferroelectric phase-transition temperature of croconic acid is over 150 °C, the highest value among the low-molecular-weight organic ferroelectrics, and croconic acid exhibits stable ferroelectricity at room temperature. The discovery that the organic compound known for over 180 years exhibits strong ferroelectricity suggests that other organic compound may have ferroelectricity as strong as those of inorganic ferroelectrics. Hence, this discovery is expected to encourage the development of ferroelectric organic materials.
The details of this research will be published in the February 11 issue of "Nature," an international scientific journal.